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8 Mar 2004

Volume 84, Issue 10, pp. 1623-1807

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Appl. Phys. Lett. 84, 1798 (2004); http://dx.doi.org/10.1063/1.1664019 (3 pages)

Bartosz A. Grzybowski, Michal Radkowski, Christopher J. Campbell, Jessamine Ng Lee, and George M. Whitesides
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Photoluminescence in quantum-confined SnO2 nanocrystals: Evidence of free exciton decay

E. J. H. Lee, C. Ribeiro, T. R. Giraldi, E. Longo, E. R. Leite, and J. A. Varela

Appl. Phys. Lett. 84, 1745 (2004); http://dx.doi.org/10.1063/1.1655693 (3 pages) | Cited 79 times

Online Publication Date: 2 March 2004

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Nanocrystalline SnO2 quantum dots were synthesized at room temperature by hydrolysis reaction of SnCl2. The addition of tetrabutyl ammonium hydroxide and the use of hydrothermal treatment enabled one to obtain tin dioxide colloidal suspensions with mean particle radii ranging from 1.5 to 4.3 nm. The photoluminescent properties of the suspensions were studied. The particle size distribution was estimated by transmission electron microscopy. Assuming that the maximum intensity photon energy of the photoluminescence spectra is related to the band gap energy of the system, the size dependence of the band gap energies of the quantum-confined SnO2 particles was studied. This dependence was observed to agree very well with the weak confinement regime predicted by the effective mass model. This might be an indication that photoluminescence occurs as a result of a free exciton decay process. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
61.46.-w Structure of nanoscale materials
73.21.La Quantum dots
78.55.Hx Other solid inorganic materials
71.35.Gg Exciton-mediated interactions
73.22.Lp Collective excitations
68.37.Lp Transmission electron microscopy (TEM)

Nanometer-sized antenna for enhancement of absorption of light by dye molecules

Vladimir P. Zhdanov and Bengt Kasemo

Appl. Phys. Lett. 84, 1748 (2004); http://dx.doi.org/10.1063/1.1667268 (2 pages) | Cited 1 time

Online Publication Date: 2 March 2004

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One of the ways to increase the absorbance of dye molecules is to optimize the property of their environment. In particular, a dye molecule can be surrounded by a few other molecules absorbing at lower frequencies. Our analysis indicates that the amplification factor of such nanometer-sized antennas may be up to about 200. © 2004 American Institute of Physics.
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78.20.-e Optical properties of bulk materials and thin films
61.46.-w Structure of nanoscale materials
42.70.Jk Polymers and organics

Mechanism of bright selective imaging of single-walled carbon nanotubes on insulators by scanning electron microscopy

Yoshikazu Homma, Satoru Suzuki, Yoshihiro Kobayashi, Masao Nagase, and Daisuke Takagi

Appl. Phys. Lett. 84, 1750 (2004); http://dx.doi.org/10.1063/1.1667608 (3 pages) | Cited 50 times

Online Publication Date: 2 March 2004

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Individual single-walled carbon nanotubes (SWNTs) produce highly bright images of the insulator surface around them when observed by scanning electron microscopy at low primary-electron voltage. We found that the insulator surface near SWNTs emits more secondary electrons due to electrons supplied through SWNTs connecting to the outside area of the primary-electron beam scanning. SWNTs are thus highlighted as bright lines corresponding to the electron-beam-induced current range around them. This technique provides a useful and effective way to investigate lateral growth morphology of SWNTs on the substrate. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Formation of air stable carbon-skinned iron nanocrystals from FeC2

Kentaroh Kosugi, M. Junaid Bushiri, and Nobuyuki Nishi

Appl. Phys. Lett. 84, 1753 (2004); http://dx.doi.org/10.1063/1.1666995 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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Charge neutralization reaction in ionic salt of Fe2+C22− is found to produce carbon-skinned Fe nanocrystals. FeC2 is formed as an intermediate product in the reaction of FeCl2 solved in acetonitrile with CaC2 fine powder and also able to be isolated as black nanocrystals. Heating of FeC2 at temperature higher than 250 °C induces segregation of metallic iron. The segregated carbons grow as graphitic sheets parallel to the growing Fe lattice plane. This direct bonding is due to an accidental matching of the Fe–Fe distance (2.866 Å) with that of the C1–C4 distance (2.842 Å) of the hexagonal rings in graphite. The x-ray diffraction pattern indicates that the particles are composed of α-Fe and graphitic carbon. The thickness of the skin is almost constant as thick as 3.5 nm independent of the body size. The particles with an average size of 30 nm exhibit temperature dependence of the magnetic cohesive force as function of T−0.275. © 2004 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
81.07.Bc Nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments

Atom-resolved scanning tunneling microscopy of (In,Ga)As quantum wires on GaAs(311)A

H. Wen, Z. M. Wang, and G. J. Salamo

Appl. Phys. Lett. 84, 1756 (2004); http://dx.doi.org/10.1063/1.1664018 (3 pages) | Cited 16 times

Online Publication Date: 2 March 2004

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Generally (In,Ga)As strained growth on GaAs surfaces results in zero-dimensional quantum dots. The formation of one-dimensional quantum wires is demonstrated during (In,Ga)As molecular-beam-epitaxial growth on GaAs(311)A at high temperature. The wires are running along the [−233] direction. Atomically resolved scanning tunneling microscopy images reveal that the wires are triangular-shaped in cross section and the two side bonding facets are {11,5,2}. These results are discussed in terms of a mechanism of strain-driven facet formation. © 2004 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.05.Ea III-V semiconductors
68.65.La Quantum wires (patterned in quantum wells)
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

In situ control of the catalyst efficiency in chemical vapor deposition of vertically aligned carbon nanotubes on predeposited metal catalyst films

Gyula Eres, A. A. Puretzky, D. B. Geohegan, and H. Cui

Appl. Phys. Lett. 84, 1759 (2004); http://dx.doi.org/10.1063/1.1668325 (3 pages) | Cited 44 times

Online Publication Date: 2 March 2004

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Premature termination of growth, presumably because of catalyst deactivation, is an undesirable side effect of chemical vapor deposition of vertically aligned carbon nanotubes on predeposited metal catalyst films. The addition of ferrocene, an effective precursor for in situ Fe formation, was found to enhance carbon nanotube growth rates and extend growth to 3.25 mm thick carbon nanotube films. Ferrocene was introduced into the gas stream by thermal evaporation concurrently with acetylene using a specially constructed source. The key factor facilitating the growth of thick carbon nanotube films was the independent and precise control of the ferrocene amount in the feedstock. The carbon nanotube films were characterized by scanning and transmission electron microscopy, and Raman spectroscopy. The temperature dependence of the carbon nanotube growth with ferrocene exhibits a steep drop at high substrate temperatures and a loss of vertical alignment at 900 °C. The negative temperature coefficient of the growth rate suggests that the reaction mechanism of vertically aligned carbon nanotube growth is governed by a heterogeneous intermediate step. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
78.30.Na Fullerenes and related materials

On the modeling of lattice thermal conductivity in semiconductor quantum dot superlattices

Alexander Khitun, Jianlin Liu, and Kang L. Wang

Appl. Phys. Lett. 84, 1762 (2004); http://dx.doi.org/10.1063/1.1668317 (3 pages) | Cited 6 times

Online Publication Date: 2 March 2004

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We present a theoretical model for the cross-plane lattice thermal conductivity calculations in semiconductor quantum dot superlattices. Based on continuum approximation, our model takes into account scattering of acoustic phonons on quantum dots. In most practical cases, the dot volume fraction is relatively small and/or dot and host materials have a small acoustic mismatch. This fact lets us take into account only first order scattering events and to significantly simplify the calculations. The results of numerical simulations carried out for Si/Ge quantum dot superlattices show good agreement with experimental data. The proposed model is useful for many applications recently suggested for semiconductor quantum-dot superlattices. © 2004 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.65.Cd Superlattices
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Controlling energy dissipation and stability of micromechanical silicon resonators with self-assembled monolayers

Joshua A. Henry, Yu Wang, and Melissa A. Hines

Appl. Phys. Lett. 84, 1765 (2004); http://dx.doi.org/10.1063/1.1664015 (3 pages) | Cited 9 times

Online Publication Date: 2 March 2004

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Self-assembled alkyl monolayers that are directly tethered to the silicon surface with a Si–C bond suppress mechanical energy dissipation in megahertz-range micromechanical silicon oscillators as compared to the more common silicon oxide coating. Although not as low loss as freshly prepared H-terminated surfaces, Si–C tethered monolayers are more stable with time. Alkyl monolayers derived from chlorosilanes have much poorer mechanical performance. Both types of monolayers suppress adsorption. © 2004 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.Dn Self-assembly
07.10.Cm Micromechanical devices and systems

Application of tip-enhanced microscopy for nonlinear Raman spectroscopy

Taro Ichimura, Norihiko Hayazawa, Mamoru Hashimoto, Yasushi Inouye, and Satoshi Kawata

Appl. Phys. Lett. 84, 1768 (2004); http://dx.doi.org/10.1063/1.1647277 (3 pages) | Cited 18 times

Online Publication Date: 2 March 2004

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A tip-enhanced electric field at a metallic probe tip of apertureless near-field scanning optical microscope was applied to a third-order nonlinear optical process, coherent anti-Stokes Raman spectroscopy. The combination of the enhanced field and third-order nonlinearity resolved molecular vibrations of adenine molecules embedded in deoxyribonucleic acid double-helix nanocrystals beyond the diffraction limit of light. © 2004 American Institute of Physics.
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87.14.G- Nucleic acids
78.30.Jw Organic compounds, polymers
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
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