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24 May 2004

Volume 84, Issue 21, pp. 4141-4340

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4316 (2004); http://dx.doi.org/10.1063/1.1756684 (3 pages)

Seok Pil Jang and Stephen U. S. Choi
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Control of surface roughness in amorphous thin-film growth

F. Elsholz, E. Schöll, and A. Rosenfeld

Appl. Phys. Lett. 84, 4167 (2004); http://dx.doi.org/10.1063/1.1755425 (3 pages) | Cited 21 times

Online Publication Date: 6 May 2004

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The growth of optical layers of SiO2 and Nb2O5 on amorphous substrates is investigated. We develop a kinetic Monte Carlo model which mimics the amorphous structure by randomly fluctuating binding energies. The resulting surface profiles are characterized by their root-mean-square roughness, height–height correlation functions, and growth exponents. For strong random fluctuations, the growth exponents exceed the value of 0.5, in good agreement with experiment. © 2004 American Institute of Physics.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Cd Deposition by sputtering
68.37.Ps Atomic force microscopy (AFM)
68.35.Ct Interface structure and roughness
85.40.Sz Deposition technology

Growth and transport properties of complementary germanium nanowire field-effect transistors

Andrew B. Greytak, Lincoln J. Lauhon, Mark S. Gudiksen, and Charles M. Lieber

Appl. Phys. Lett. 84, 4176 (2004); http://dx.doi.org/10.1063/1.1755846 (3 pages) | Cited 141 times

Online Publication Date: 6 May 2004

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n- and p-type Ge nanowires were synthesized by a multistep process in which axial elongation, via vapor–liquid–solid (VLS) growth, and doping were accomplished in separate chemical vapor deposition steps. Intrinsic, single-crystal, Ge nanowires prepared by Au nanocluster-mediated VLS growth were surface-doped in situ using diborane or phosphine, and then radial growth of an epitaxial Ge shell was used to cap the dopant layer. Field-effect transistors prepared from these Ge nanowires exhibited on currents and transconductances up to 850 μA/μm and 4.9 μA/V, respectively, with device yields of >85%. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.63.Nm Quantum wires
61.46.-w Structure of nanoscale materials

Brillouin observation of bulk and confined acoustic waves in silica microspheres

H. S. Lim, M. H. Kuok, S. C. Ng, and Z. K. Wang

Appl. Phys. Lett. 84, 4182 (2004); http://dx.doi.org/10.1063/1.1756206 (3 pages) | Cited 18 times

Online Publication Date: 6 May 2004

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Brillouin scattering from loose silica microspheres has been investigated as a function of their diameter (140 nm to 4 μm). The measured linear dependence of the confined acoustic mode frequencies on the inverse sphere diameters accords well with Lamb’s theory. Bulk acoustic modes are also observed in the larger microspheres, suggesting that the limiting size of a particle for these modes to be observable is about three times their wavelength. Internal consistency in the analyses of the bulk and confined mode data shows the validity of this Brillouin technique in the evaluation of the elastic properties of microspheres. Additionally it also affords a means of sizing the diameters of microspheres. © 2004 American Institute of Physics.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Vs Fine-particle systems
62.30.+d Mechanical and elastic waves; vibrations

Magneto-optical Kerr effect in Fe21Ni79 films on Si(100): Quantum behavior for film thicknesses below ∼6 nm

J. M. Talmadge, J. Gao, M. P. Riley, R. J. Roth, S.-O. Kim, J. G. Eden, F. A. Pudonin, and I. V. Mel’nikov

Appl. Phys. Lett. 84, 4197 (2004); http://dx.doi.org/10.1063/1.1737465 (3 pages) | Cited 2 times

Online Publication Date: 7 May 2004

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The magneto-optical Kerr effect (MOKE) has been observed and characterized in 1–80 nm thick Fe21Ni79 films deposited onto Si(100), for an external magnetic field (variable in strength up to 400 G) oriented parallel or orthogonal to the magnetization axis of the film. A measurable response is observed for film thicknesses (d) as small as 2 nm and, if the external magnetic field lies in the plane of the film, two-dimensional quantum behavior is evident for d≲6 nm. A precipitous decline in the magnitude of the MOKE response is accompanied by an increase in the coercivity and, when the external field is perpendicular to the film magnetization axis, a rapid rise in the saturation field. Experiments also confirm the existence of a component of the film magnetization oriented out of the plane of the film, a result consistent with the prediction of computational studies [T. Trunk et al., J. Appl. Phys. 89, 7606 (2001)] that the transition between Bloch and Néel wall domain structure occurs in FeNi films for film thicknesses of ≈30 nm. © 2004 American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Dip-pen nanopatterning of photosensitive conducting polymer using a monomer ink

Ming Su, Mohammed Aslam, Lei Fu, Nianqiang Wu, and Vinayak P. Dravid

Appl. Phys. Lett. 84, 4200 (2004); http://dx.doi.org/10.1063/1.1737469 (3 pages) | Cited 29 times

Online Publication Date: 7 May 2004

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Controlled patterning of conducting polymers at a micro- or nanoscale is the first step towards the fabrication of miniaturized functional devices. Here, we introduce an approach for the nanopatterning of conducting polymers using an improved monomer “ink” in dip-pen nanolithography (DPN). The nominal monomer “ink” is converted, in situ, to its conducting solid-state polymeric form after patterned. Proof-of-concept experiments have been performed with acid-promoted polymerization of pyrrole in a less reactive environment (tetrahydrofuran). The ratios of reactants are optimized to give an appropriate rate to match the operation of DPN. A similar synthesis process for the same polymer in its bulk form shows a high conductance and crystalline structure. The miniaturized conducting polymer sensors with light detection ability are fabricated by DPN using the improved ink formula, and exhibit excellent response, recovery, and sensitivity parameters. © 2004 American Institute of Physics.
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82.35.Cd Conducting polymers
85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
82.50.-m Photochemistry
78.40.Me Organic compounds and polymers
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Effects of stacking on the structural and optical properties of self-organized GaN/AlN quantum dots

N. Gogneau, F. Fossard, E. Monroy, S. Monnoye, H. Mank, and B. Daudin

Appl. Phys. Lett. 84, 4224 (2004); http://dx.doi.org/10.1063/1.1755840 (3 pages) | Cited 18 times

Online Publication Date: 7 May 2004

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We report on the effect of vertical correlation on GaN/AlN quantum dots grown by plasma-assisted molecular-beam epitaxy using the modified Stranski–Krastanow growth mode. When increasing the number of GaN periods, we observe a homogenization of the island distribution and a redshift of the luminescence line. This redshift is attributed to an increase of the quantum Stark effect due to the increase of the piezoelectric contribution to the internal electric field. © 2004 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
77.65.Bn Piezoelectric and electrostrictive constants
78.20.Jq Electro-optical effects
78.55.Hx Other solid inorganic materials

Thermal conductivity improvement of silicone elastomer with carbon nanotube loading

C. H. Liu, H. Huang, Y. Wu, and S. S. Fan

Appl. Phys. Lett. 84, 4248 (2004); http://dx.doi.org/10.1063/1.1756680 (3 pages) | Cited 65 times

Online Publication Date: 7 May 2004

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Unpurified carbon nanotubes were introduced to silicone elastomer to investigate their effect on the thermal conductivity. Microstructure studies by a scanning electron microscope showed that the carbon nanotubes (CNTs) can be well dispersed in the matrix by the grinding method. No notable agglomerates or phase separation between the carbon and silicone matrix were observed, and the CNTs were individually in random orientation. The thermal conductivities of the composites were measured with the ASTM (American Society of Testing Materials) D5470 method. The thermal conductivities κ were found to increase with the carbon amount. There was a 65% enhancement in κ with 3.8 wt % CNT loading. The enhancement by equal loading of carbon black was found to be a little lower than that by the CNT loading. The composites loaded with CNTs displayed an abrupt increase in the electrical conductivity. © 2004 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
61.46.-w Structure of nanoscale materials

Scanning tunneling spectroscopy of suspended single-wall carbon nanotubes

B. J. LeRoy, S. G. Lemay, J. Kong, and C. Dekker

Appl. Phys. Lett. 84, 4280 (2004); http://dx.doi.org/10.1063/1.1748836 (3 pages) | Cited 17 times

Online Publication Date: 7 May 2004

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We have performed low-temperature scanning tunneling microscopy measurements on single-wall carbon nanotubes that are freely suspended over a trench. The nanotubes were grown by chemical vapor deposition on a Pt substrate with predefined trenches etched into it. Atomic resolution was obtained on the freestanding portions of the nanotubes. Spatially resolved spectroscopy on the suspended portion of both metallic and semiconducting nanotubes was also achieved, showing a Coulomb-staircase behavior superimposed on the local density of states. The spacing of the Coulomb blockade peaks changed with tip position reflecting a changing tip-tube capacitance. © 2004 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Efficient excitation transfer from polymer to nanocrystals

Tung-Wah Frederick Chang, Sergei Musikhin, Ludmila Bakueva, Larissa Levina, Margaret A. Hines, Paul W. Cyr, and Edward H. Sargent

Appl. Phys. Lett. 84, 4295 (2004); http://dx.doi.org/10.1063/1.1755414 (3 pages) | Cited 40 times

Online Publication Date: 7 May 2004

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We quantify experimentally the efficiency of excitation transfer from a semiconducting polymer matrix to quantum dot nanocrystals. We study 5±0.5 nm PbS nanocrystals embedded in MEH-PPV (poly[2-methoxy-5-(2′-ethylhexyloxy-p-phenylenevinylene)]) polymer. We determine the excitation transfer efficiency from normalized photoluminescence excitation measurements. When the composites are made using as-synthesized PbS nanocrystals capped by oleate ligands, the excitation transfer efficiency is about 20%. Replacing these ligands with shorter chains results in a factor-of-3 enhancement in the excitation transfer efficiency. Our findings provide guidance to the realization of efficient electroluminescent devices. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Hx Other solid inorganic materials
85.60.-q Optoelectronic devices
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Role of Brownian motion in the enhanced thermal conductivity of nanofluids

Seok Pil Jang and Stephen U. S. Choi

Appl. Phys. Lett. 84, 4316 (2004); http://dx.doi.org/10.1063/1.1756684 (3 pages) | Cited 44 times

Online Publication Date: 7 May 2004

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We have found that the Brownian motion of nanoparticles at the molecular and nanoscale level is a key mechanism governing the thermal behavior of nanoparticle–fluid suspensions (“nanofluids”). We have devised a theoretical model that accounts for the fundamental role of dynamic nanoparticles in nanofluids. The model not only captures the concentration and temperature-dependent conductivity, but also predicts strongly size-dependent conductivity. Furthermore, we have discovered a fundamental difference between solid/solid composites and solid/liquid suspensions in size-dependent conductivity. This understanding could lead to design of nanoengineered next-generation coolants with industrial and biomedical applications in high-heat-flux cooling. © 2004 American Institute of Physics.
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82.70.Kj Emulsions and suspensions
66.25.+g Thermal conduction in nonmetallic liquids

Formation of SiGe nanocrystals in HfO2 using in situ chemical vapor deposition for memory applications

Rohit Gupta, Won Jong Yoo, Yingqian Wang, Zerlinda Tan, Ganesh Samudra, Sungjoo Lee, Daniel S. H. Chan, Kian Ping Loh, L. K. Bera, N. Balasubramanian, and Dim-Lee Kwong

Appl. Phys. Lett. 84, 4331 (2004); http://dx.doi.org/10.1063/1.1758297 (3 pages) | Cited 13 times

Online Publication Date: 7 May 2004

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The in situ deposition process of SiGe nanocrystals on SiO2 and HfO2 substrates was studied using Auger electron spectroscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. The Ge concentration in SiGe nanocrystals increased with deposition time at equal Si/Ge flow rates. Analysis indicated that the nucleation of Ge takes place preferentially on prenucleated Si on the dielectric. Memory transistors were fabricated using SiGe nanocrystals and HfO2 tunneling/control dielectrics as a gate stack. Memory effects from floating SiGe nanocrystals in HfO2 were clearly observed at room temperature from metal–oxide–semiconductor field effect transistor devices with a threshold voltage shift of about 0.5 V with the application of +4 V. © 2004 American Institute of Physics.
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81.05.Hd Other semiconductors
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.37.Ps Atomic force microscopy (AFM)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
85.30.Tv Field effect devices
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