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2 Feb 2009

Volume 94, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 059901 (2009); http://dx.doi.org/10.1063/1.3086725 (3 pages)

Yuta Tsukada, Tsuyoshi Honma, and Takayuki Komatsu
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Effects of thermal annealing on the emission properties of type-II InAs/GaAsSb quantum dots

Yu-An Liao, Wei-Ting Hsu, Pei-Chin Chiu, Jen-Inn Chyi, and Wen-Hao Chang

Appl. Phys. Lett. 94, 053101 (2009); http://dx.doi.org/10.1063/1.3062979 (3 pages) | Cited 12 times

Online Publication Date: 2 February 2009

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We report the effects of thermal annealing on the emission properties of type-II InAs quantum dots (QDs) covered by a thin GaAs1−xSbx layer. Apart from large blueshifts and a pronounced narrowing of the QD emission peak, the annealing induced alloy intermixing also leads to enhanced radiative recombination rates and reduced localized states in the GaAsSb layer. Evidences of the evolution from type-II to type-I band alignments are obtained from time-resolved and power-dependent photoluminescence measurements. We demonstrate that postgrowth thermal annealing can be used to tailor the band alignment, the wave function overlaps, and hence the recombination dynamics in the InAs/GaAsSb type-II QDs.
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78.67.Hc Quantum dots
61.72.Cc Kinetics of defect formation and annealing
73.20.Fz Weak or Anderson localization
78.47.jd Time resolved luminescence
73.21.La Quantum dots
78.55.Cr III-V semiconductors

Planar hybrid superlattices by compression of rolled-up nanomembranes

T. Zander, Ch. Deneke, A. Malachias, Ch. Mickel, T. H. Metzger, and O. G. Schmidt

Appl. Phys. Lett. 94, 053102 (2009); http://dx.doi.org/10.1063/1.3074449 (3 pages) | Cited 4 times

Online Publication Date: 2 February 2009

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Hybrid metal/semiconductor superlattices are obtained by the controlled compression of rolled-up metal/semiconductor nanomembranes. The planar superlattice maintains the crystalline quality of the semiconductor and the polycrystalline texture of the metal, allowing the integration of these materials into a multilayer system that cannot be produced by any direct deposition procedure. The superlattice consists of two symmetrically inverted multilayer stacks splitted by a metallic mirror plane. Additional intensity peaks in x-ray reflectivity confirm the periodic structure created by the roll up and compression of nanomembranes.
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68.65.Cd Superlattices
73.40.Ns Metal-nonmetal contacts
61.46.-w Structure of nanoscale materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Modeling thermal decay of high-aspect-ratio nanostructures

Marcos F. Castez and Roberto C. Salvarezza

Appl. Phys. Lett. 94, 053103 (2009); http://dx.doi.org/10.1063/1.3077030 (3 pages) | Cited 3 times

Online Publication Date: 2 February 2009

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A multiapproach modeling of surface diffusion driven decay of three dimensional high-aspect-ratio nanostructures is presented. Three different strategies are used: a continuous model, kinetic Monte Carlo simulations, and a molecular dynamics approach using an embedded atom model potential. All these models predict that an initially single-valued surface evolves into an intermediate multivalued state, in which features on the surface develop into a nonconvex shape. Moreover, such nanofeatures in the case of discrete models are quite well described in terms of the continuous modeling. Quantitative bounds for the aspect-ratios in which emergence of overhangs starts are estimated.
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68.35.Fx Diffusion; interface formation

Focused patterning of nanoparticles by controlling electric field induced particle motion

Heechul Lee, Sukbeom You, Chang Gyu Woo, Kyunghoon Lim, Kimin Jun, and Mansoo Choi

Appl. Phys. Lett. 94, 053104 (2009); http://dx.doi.org/10.1063/1.3077158 (3 pages) | Cited 7 times

Online Publication Date: 2 February 2009

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We report a general methodology for producing focused arrays of nanoparticles via electrodynamic focusing approach and controlling the inertial effect of charged aerosols. An important effect of particle inertia is identified and verified by performing detailed calculations of electric field induced particle motion and experimenting with electrosprayed nanoparticles. The controllability of focusing is demonstrated by changing the curvature of electric field lines.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Rf Micro- and nanoscale pattern formation
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.70.Rr Aerosols and foams

Controlled dielectrophoretic assembly of carbon nanotubes using real-time electrical detection

Sebastian Sorgenfrei, Inanc Meric, Sarbajit Banerjee, Austin Akey, Sami Rosenblatt, Irving P. Herman, and Kenneth L. Shepard

Appl. Phys. Lett. 94, 053105 (2009); http://dx.doi.org/10.1063/1.3077620 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2009

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We investigate dielectrophoretic deposition of single-walled carbon nanotubes using an in situ detection system. Pairs of electrodes are stimulated with a small-amplitude, low-frequency voltage superimposed on a large-amplitude, high-frequency dielectrophoretic voltage. Measuring the magnitude of the current both at dc (Idc) and at the low frequency (Iac) through a digital lock-in technique allows us to determine when a nanotube has made electrical contact and to halt the dielectrophoretic process. Because Idc is determined by nonlinearities in the device current-voltage characteristic, measurement of the Idc/Iac ratio allows the real-time determination of whether the deposited nanotube is metallic or semiconducting.
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82.45.Yz Nanostructured materials in electrochemistry
73.40.-c Electronic transport in interface structures
73.63.Rt Nanoscale contacts
82.45.Fk Electrodes
85.35.Kt Nanotube devices
81.15.Pq Electrodeposition, electroplating
73.63.Fg Nanotubes

Thickness-gradient dependent Raman enhancement in silver island films

T. W. H. Oates and S. Noda

Appl. Phys. Lett. 94, 053106 (2009); http://dx.doi.org/10.1063/1.3078272 (3 pages) | Cited 4 times

Online Publication Date: 2 February 2009

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We show evidence of a dependence of the enhancement of the Raman scattering cross section on the length of the gradient in graded silver island films. A factor-of-three increase in the Raman signal is observed for gradients with length of the order of 0.5 mm when compared to gradients of the order of 9 mm. Scanning electron microscopy reveals the nanostructure of the two films to be statistically similar. We attribute the observation to differences in plasmon hybridization in the gradients arising from long range structural differences.
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78.66.Bz Metals and metallic alloys
78.30.Er Solid metals and alloys
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Rotational friction of single-wall carbon nanotubes in liquid suspension

Frank M. Zimmermann and Jerry W. Shan

Appl. Phys. Lett. 94, 053107 (2009); http://dx.doi.org/10.1063/1.3033365 (3 pages) | Cited 1 time

Online Publication Date: 3 February 2009

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The hydrodynamics of single-wall carbon nanotubes rotated in liquid suspension by an external electric field was experimentally investigated with laser polarimetry and compared with theoretical predictions. The measured rates of change of the nematic order parameter were largely consistent with theoretical predictions based on classical, no-slip hydrodynamics. This implies that, despite the nanotubes’ diameter approaching the size of the solvent molecules and the reduced resistance previously reported for internal flow through carbon nanotubes, classical continuum hydrodynamics holds approximately for external flow about individual single-wall carbon nanotubes in liquids.
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82.70.Kj Emulsions and suspensions
62.10.+s Mechanical properties of liquids
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Clean superconducting In nanowires encapsulated within insulating ZnS nanotubes

Goutam Sheet, Ujjal K. Gautam, Ajay D. Thakur, Kazuto Hirata, Yoshio Bando, and Tomonobu Nakayama

Appl. Phys. Lett. 94, 053108 (2009); http://dx.doi.org/10.1063/1.3072359 (3 pages) | Cited 4 times

Online Publication Date: 3 February 2009

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We have synthesized indium (In) nanowires in pure form and large scale, encapsulated within insulating ZnS nanotubes, and examined the intrinsic superconductivity in one-dimensional limit. We demonstrate that the property of the superconducting nanowires encapsulated within insulating nanotubes can be controlled down to diameters much smaller than the characteristic lengths. The critical temperature and critical magnetic field of the one-dimensional In nanowires are not affected down to a diameter of 40 nm, almost 10% of the coherence length of bulk In. This study further suggests that superconducting interconnects, with controlled physical properties, in nanocircuits could be achieved by such encapsulation.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation
74.25.Ha Magnetic properties including vortex structures and related phenomena

Direct printing of aligned carbon nanotube patterns for high-performance thin film devices

Jiwoon Im, Il-Ha Lee, Byung Yang Lee, Byeongju Kim, June Park, Woojong Yu, Un Jeong Kim, Young Hee Lee, Maeng-Je Seong, Eun Hong Lee, Yo-Sep Min, and Seunghun Hong

Appl. Phys. Lett. 94, 053109 (2009); http://dx.doi.org/10.1063/1.3073748 (3 pages) | Cited 6 times

Online Publication Date: 3 February 2009

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The aligned assembly of carbon nanotubes (CNTs) on substrate presents a significant bottleneck in the fabrication of high-performance thin film devices. Here, we report a direct printing method to prepare laterally aligned thick CNT patterns over large surface regions. In this method, CNT forests were grown selectively on specific regions of one substrate, and the forest patterns were transferred on another SiO2 substrate in a laterally aligned formation while keeping their original shapes. The degree of alignment was characterized via electrical measurement and polarized Raman spectroscopy. Furthermore, we demonstrated high-performance field-effect transistors and gas sensors using our method.
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81.16.Rf Micro- and nanoscale pattern formation
73.63.Fg Nanotubes
85.30.Tv Field effect devices
78.30.Na Fullerenes and related materials

High-yield dielectrophoretic assembly of two-dimensional graphene nanostructures

Brian R. Burg, Fabian Lütolf, Julian Schneider, Niklas C. Schirmer, Timo Schwamb, and Dimos Poulikakos

Appl. Phys. Lett. 94, 053110 (2009); http://dx.doi.org/10.1063/1.3077197 (3 pages) | Cited 14 times

Online Publication Date: 3 February 2009

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Graphene handling is still dominated by serial mechanical exfoliation, which may well facilitate measurements in a laboratory environment but does not allow reliable larger-scale integration. Herein we demonstrate the controlled, high-yield (>90%), site-selective deposition of ultrathin few-layer (three to ten) graphene oxide by dielectrophoresis between prefabricated electrodes. Individual layers are found near the edges. Initially insulating, thermal reduction at 450 °C thins out the two-dimensional few-atom thick films and dramatically reduces electrical resistances down to 40 kΩ. Conductivities between 15 and 36 S/cm are obtained. The introduced method permits the nonintrusive, parallel, large-scale assembly of soluble two-dimensional nanostructures and sheets.
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82.45.Yz Nanostructured materials in electrochemistry
81.05.U- Carbon/carbon-based materials
81.07.Bc Nanocrystalline materials

Effects of electron-beam irradiation on conducting polypyrrole nanowires

Young Ki Hong, Dong Hyuk Park, Se Hee Park, Soung Kyu Park, and Jinsoo Joo

Appl. Phys. Lett. 94, 053111 (2009); http://dx.doi.org/10.1063/1.3077589 (3 pages) | Cited 5 times

Online Publication Date: 3 February 2009

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Conducting polypyrrole (PPy) nanowires (NWs) were irradiated by a relatively high energy (300 keV–2 MeV) electron-beam (e-beam) generated from a linear electron accelerator in an atmospheric environment. From the current-voltage characteristics of pristine and 2 MeV e-beam irradiated PPy NWs, we observed a dramatic variation in resistance from 8.0×102 to 1.45×108 Ω, that is, we observed a transition from conducting states to nonconducting states through the e-beam irradiation. To discern conformational changes and the doping states of PPy NWs through the e-beam irradiation, we measured Raman and ultraviolet-visible absorption spectra for the PPy NWs. As the energy of the e-beam irradiation increased, we observed that the PPy NWs were changed from doping states to dedoping states with conformational modification including the variation in π-conjugation length.
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73.61.Ph Polymers; organic compounds
61.80.Fe Electron and positron radiation effects
61.72.up Other materials
78.67.Lt Quantum wires
73.63.Nm Quantum wires

Room-temperature-operating carbon nanotube single-hole transistors with significantly small gate and tunnel capacitances

Yasuhide Ohno, Yoshihiro Asai, Kenzo Maehashi, Koichi Inoue, and Kazuhiko Matsumoto

Appl. Phys. Lett. 94, 053112 (2009); http://dx.doi.org/10.1063/1.3078234 (3 pages) | Cited 15 times

Online Publication Date: 3 February 2009

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Carbon nanotube single-hole transistors operating at room temperature were realized. To obtain large charging energy, a 25-nm-long carbon nanotube channel was formed by shadow evaporation for small gate capacitance and an insulator was inserted between the channel and electrodes for small tunnel capacitances. A significantly small gate capacitance (0.06 aF) and a small tunnel capacitance (0.3 aF) were obtained. The estimated charging energy of a carbon nanotube single quantum dot was 108 meV. Drain current oscillation as a function of gate voltage was clearly observed while typical p-type field effect transistor characteristics were obtained for the device without insulator. These results indicate that the small tunnel capacitance is necessary for the room-temperature-operating carbon nanotube single-charge transistors.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices
85.35.Gv Single electron devices

Top-down approach to align single-walled carbon nanotubes on silicon substrate

Carlo M. Orofeo, Hiroki Ago, Naoki Yoshihara, and Masaharu Tsuji

Appl. Phys. Lett. 94, 053113 (2009); http://dx.doi.org/10.1063/1.3078280 (3 pages) | Cited 9 times

Online Publication Date: 3 February 2009

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We report controlled horizontal alignment of single-walled carbon nanotubes (SWNTs) directly grown on trenched SiO2/Si substrate. The nanotubes were found to align along the trenches, which were created via electron beam lithography followed by reactive ion etching. From the experimental observations, the alignment mechanism was proposed. Furthermore, field-effect transistors fabricated from these substrates showed acceptable mobility and on/off ratio as high as 104. The method offers the possibility of large-scale integrated SWNT electronics for mass production.
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81.16.Nd Micro- and nanolithography
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
85.35.Kt Nanotube devices

In situ small-angle x-ray scattering study of nanostructure evolution during decomposition of arc evaporated TiAlN coatings

M. Odén, L. Rogström, A. Knutsson, M. R. Terner, P. Hedström, J. Almer, and J. Ilavsky

Appl. Phys. Lett. 94, 053114 (2009); http://dx.doi.org/10.1063/1.3078283 (3 pages) | Cited 12 times

Online Publication Date: 3 February 2009

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Small-angle x-ray scattering was used to study in situ decomposition of an arc evaporated TiAlN coating into cubic-TiN and cubic-AlN particles at elevated temperature. At the early stages of decomposition particles with ellipsoidal shape form, which grow and change shape to spherical particles at higher temperatures. The spherical particles grow at a rate of 0.18 Å/°C while coalescing.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.70.Ck X-ray scattering
81.07.Bc Nanocrystalline materials
68.55.-a Thin film structure and morphology

Electronic localization and optical absorption in embedded silicon nanograins

Luigi Bagolini, Alessandro Mattoni, and Luciano Colombo

Appl. Phys. Lett. 94, 053115 (2009); http://dx.doi.org/10.1063/1.3078281 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2009

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We study the spatial distribution of electron states in crystalline Si nanograins embedded into amorphous silicon. We prove that it is not possible to tune the absorption gap by only controlling the size of the grain, since no quantum confinement there occurs. The absorption properties of such a two-phase system are rather controlled by the population of localized electron states generated by large angular distortions of Si–Si bonds.
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73.22.-f Electronic structure of nanoscale materials and related systems
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
61.46.Hk Nanocrystals
71.20.Mq Elemental semiconductors

Electrical depth profiling in thin SiON layers

A. Rozenblat, Y. Rosenwaks, L. Segev, and H. Cohen

Appl. Phys. Lett. 94, 053116 (2009); http://dx.doi.org/10.1063/1.3073050 (3 pages) | Cited 3 times

Online Publication Date: 5 February 2009

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The internal structure of SiON films is extracted electrically, demonstrating an efficient, noncontact, nondestructive means for depth compositional analysis in gate oxides. The electrical data, obtained using x-ray photoelectron spectroscopy (XPS) based controlled surface charging (CSC), are compared with independent time of flight secondary ion mass spectroscopy and angle resolved XPS data. Inhomogeneous composition with significant nitrogen enrichment at the top of the oxide layer is observed. Capabilities of the CSC method in treating heterostructures of poor chemical contrast are discussed.
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68.55.ag Semiconductors
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Cu-doping effects in CdI2 layered nanostructures: The role of photoinduced electron-phonon anharmonic interactions

M. Idrish Miah and J. Kasperczyk

Appl. Phys. Lett. 94, 053117 (2009); http://dx.doi.org/10.1063/1.3077171 (3 pages) | Cited 2 times

Online Publication Date: 5 February 2009

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The Cu-doping effects in CdI2 layered nanocrystals were studied experimentally. We used a photostimulated second harmonic generation (PSHG) in order to investigate the nanoconfined effects. It was found that the PSHG increased with increasing Cu-doping within a low-density limit. For the higher Cu content the PSHG output signal was decreased to the value observed for the undoped CdI2 crystal. The above results suggest that the Cu-metallic clusters play a crucial role in the processes responsible for the observed nonlinear optical effects. The large enhancement of the PSHG observed in the Cu-doped thin nanocrystals confirms the fact that the Cu-impurities of low concentrations favor stronger local photoinduced anharmonic electron-phonon interactions.
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61.72.sd Impurity concentration
63.20.Ry Anharmonic lattice modes
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.20.kd Phonon-electron interactions
63.22.Kn Clusters and nanocrystals

Control of Ge/Si intermixing during Ge island growth

Marina S. Leite, T. I. Kamins, and G. Medeiros-Ribeiro

Appl. Phys. Lett. 94, 053118 (2009); http://dx.doi.org/10.1063/1.3078289 (3 pages) | Cited 5 times

Online Publication Date: 5 February 2009

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The surface energy and growth kinetics during Ge deposition on Si(001) were modified by growing the films in a phosphine environment. Islands were formed under a H2 flux as well as in a PH3/H2 atmosphere, but the morphologies were different. The presence of PH3 not only affects the island shape and size but also the composition profile. The dramatical inhibition of Ge/Si intermixing during growth leads to islands richer in Ge compared to undoped islands.
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68.55.ag Semiconductors
68.35.Md Surface thermodynamics, surface energies
68.55.Nq Composition and phase identification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers

Dual nonlinear dielectric resonance and strong natural resonance in Ni/ZnO nanocapsules

X. G. Liu, J. J. Jiang, D. Y. Geng, B. Q. Li, Z. Han, W. Liu, and Z. D. Zhang

Appl. Phys. Lett. 94, 053119 (2009); http://dx.doi.org/10.1063/1.3079393 (3 pages) | Cited 31 times

Online Publication Date: 6 February 2009

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The electromagnetic characteristics of Ni/ZnO nanocapsules were studied at 2–18 GHz. The dual nonlinear dielectric resonance and strong natural resonance at 16.6 GHz contribute to excellent electromagnetic absorption. A reflection loss (RL) exceeding −20 dB was calculated in 14–18 GHz for an absorber thickness of 2.05 mm, and RL exceeds −10 dB in the whole X-band (10–12.4 GHz) and the whole Ku-band (12.4–18 GHz) for a thickness of 2.50 mm. The equivalent circuit model was used to explain the dual nonlinear dielectric resonance, which is ascribed to a cooperative consequence of the core/shell interfaces and the dielectric ZnO shells.
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77.22.Gm Dielectric loss and relaxation

Reducing nanoparticles in metal ablation plumes produced by two delayed short laser pulses

Sylvie Noël and Jörg Hermann

Appl. Phys. Lett. 94, 053120 (2009); http://dx.doi.org/10.1063/1.3079404 (3 pages) | Cited 18 times

Online Publication Date: 6 February 2009

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Using fast imaging and atomic force microscopy, we demonstrate that the fraction of nanoparticles in ablation plumes produced by short pulse laser irradiation of metals is strongly altered when a second laser pulse of sufficiently large delay is applied. Comparing the results obtained for gold and copper, it is shown that a significant nanoparticle reduction is only observed if the delay between both laser pulses exceeds the characteristic time of electron-lattice thermalization. We propose the reduced electronic heat transport at large lattice temperature as the dominant mechanisms for the observed nanoparticle reduction.
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52.38.Mf Laser ablation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
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