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25 Feb 2002

Volume 80, Issue 8, pp. 1319-1496

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Visible photoluminescence of Ge dots embedded in Si/SiO2 matrices

Alexander A. Shklyaev and Masakazu Ichikawa

Appl. Phys. Lett. 80, 1432 (2002); http://dx.doi.org/10.1063/1.1451986 (3 pages) | Cited 19 times

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Ge island formation on ultrathin SiO2 films enabled us to fabricate multilayer structures of Ge dots ∼6–7 nm in diameter and with an extremely high dot density of 2×1012 cm−2. Each dot had a boundary with the SiO2 film and a Si spacer layer. The multilayer structures exhibited photoluminescence (PL) with a maximum in the range of 2–3 eV depending on the excitation energy. The PL was associated with recombination between holes confined within Ge dots and electrons localized in the radiative defect centers at the Ge-dot/SiO2 interfaces. The results suggest that this recombination is much more effective than that at the Si/SiO2 interface and supported by the hole migration from the Si spacer layers to the Ge dots. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Ap Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Polymer–nanotube composites: Burying nanotubes improves their field emission properties

I. Alexandrou, E. Kymakis, and G. A. J. Amaratunga

Appl. Phys. Lett. 80, 1435 (2002); http://dx.doi.org/10.1063/1.1449537 (3 pages) | Cited 63 times

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Composite structures of single walled carbon nanotubes (SWNTs) and poly(3-octylthiophene) polymer were tested as field emitters. The structures studied were formed on n+-Si by mixing the two materials after they had been dissolved in chloroform. Three different structures were tested: (a) a SWNT mat, (b) a SWNT mat on a SWNT (30 wt %)–polymer composite and (c) a SWNT mat on pure polymer. Although the conductivity of the composite is very much lower than that of the nanotube mat, experiments show that the field emission threshold is lower and the emission current higher from structure (b) compared to the pure SWNT mat on n+-Si. A comparison between the field enhancement factors and the expected aspect ratios shows that enhancement due to an additional field enhancement mechanism other than that due to the geometrical shape of the SWNTs must exist. We propose that the field due to the surface potential modification at the triple junction between SWNTs, polymer and vacuum is adequate to create additional field emission from such sites. This mechanism can also be used to explain previously reported field emission characteristics of CNx nanocomposite films.© 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
85.35.Kt Nanotube devices
81.05.Qk Reinforced polymers and polymer-based composites
61.46.-w Structure of nanoscale materials
73.63.Fg Nanotubes

Shape preservation of Ge/Si(001) islands during Si capping

A. Rastelli, E. Müller, and H. von Känel

Appl. Phys. Lett. 80, 1438 (2002); http://dx.doi.org/10.1063/1.1453476 (3 pages) | Cited 2 times

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Coherently strained Ge/Si(001) islands were overgrown with Si at temperatures ranging from 300 to 550 °C. The induced shape changes were investigated at different stages of the capping process by scanning tunneling microscopy and high-resolution transmission electron microscopy. Islands were found to strongly flatten and intermix at temperatures above ∼ 450 °C. By contrast, a good shape preservation as well as the recovery of a flat Si surface above the buried islands can be achieved by low temperature capping at 300 °C followed by Si growth at 550 °C. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
81.05.Cy Elemental semiconductors
68.35.Ct Interface structure and roughness
68.60.Bs Mechanical and acoustical properties
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Lp Transmission electron microscopy (TEM)
68.35.Fx Diffusion; interface formation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Self-assembled carbon nanotubes grown without catalyst from nanosized carbon particles adsorbed on silicon

S. Botti, R. Ciardi, M. L. Terranova, S. Piccirillo, V. Sessa, M. Rossi, and M. Vittori-Antisari

Appl. Phys. Lett. 80, 1441 (2002); http://dx.doi.org/10.1063/1.1453485 (3 pages) | Cited 24 times

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Carbon nanotubes films have been prepared by low-velocity spraying of carbon nanosized particles on heated Si substrate. Studies reveal that by properly choosing the deposition temperature, well-aligned carbon nanotubes are self-assembled from the particles without a catalyst. Raman scattering and reflection high-energy electron diffraction show that the tubes are bundles of single-wall nanotubes. © 2002 American Institute of Physics.
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81.07.De Nanotubes
81.16.Dn Self-assembly
61.46.-w Structure of nanoscale materials
81.15.Rs Spray coating techniques
78.67.Ch Nanotubes
78.30.Na Fullerenes and related materials

Observation of size-dependent features in the photoluminescence of zinc oxide nanocrystallites by near-field ultraviolet spectroscopy

T. Yatsui, T. Kawazoe, T. Shimizu, Y. Yamamoto, M. Ueda, M. Kourogi, M. Ohtsu, and G. H. Lee

Appl. Phys. Lett. 80, 1444 (2002); http://dx.doi.org/10.1063/1.1453487 (3 pages) | Cited 18 times

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The optical properties of single zinc oxide (ZnO) nanocrystallites were investigated at room temperature by extending the optical near-field technique to the UV region. Using a UV fiber probe with a subwavelength aperture, we performed spatially- and spectrally-resolved photoluminescence (PL) imaging of individual ZnO nanocrystallites with a spatial resolution of 55 nm. Furthermore, decreasing the spot size increased the intensities of higher-energy components of the PL spectrum due to the quantum size effect. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Fluorescence intensity and color purity improvement in nanosized YBO3:Eu

Zhenggui Wei, Lingdong Sun, Chunsheng Liao, Chunhua Yan, and Shihua Huang

Appl. Phys. Lett. 80, 1447 (2002); http://dx.doi.org/10.1063/1.1452787 (3 pages) | Cited 84 times

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In order to improve the color purity of YBO3:Eu, which is practically used as a plasma phosphor, the lowering of the structural symmetry is proposed and subsequently realized in nanosized YBO3:Eu so as to increase the contribution of 5D0–7F2 transition of the luminescent centers, Eu3+ ions. Spherical YBO3:Eu nanocrystals were fabricated via thermal decomposition of complex precursors and could be crystallized at lower temperature than required by the bulks. The particle size could be controlled by adjusting the annealing temperature and time. Unlike the bulk YBO3:Eu synthesized by solid-state reaction, the quenching concentration increased with the decrease of the particle size. Furthermore, the fluorescence intensity and color purity were significantly improved in nanocrystals. Possible mechanisms responsible for these improvements were proposed. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.40.Tv Optical and dielectric properties related to treatment conditions
85.60.Pg Display systems

Electrical and thermal properties of C60-filled single-wall carbon nanotubes

J. Vavro, M. C. Llaguno, B. C. Satishkumar, D. E. Luzzi, and J. E. Fischer

Appl. Phys. Lett. 80, 1450 (2002); http://dx.doi.org/10.1063/1.1452788 (3 pages) | Cited 38 times

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We report measurements of electrical resistivity, thermopower, and thermal conductivity of highly C60-filled single-wall carbon nanotubes and unfilled controls, from 1.5 to 300 K. The data suggest that the C60 chains provide additional conductive paths for charge carriers, increase the rate of phonon scattering, and block interior sites from sorbing other gas molecules. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
73.61.Wp Fullerenes and related materials
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
72.80.Rj Fullerenes and related materials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
72.20.Pa Thermoelectric and thermomagnetic effects

Effect of cantilever–sample interaction on piezoelectric force microscopy

Seungbum Hong, Hyunjung Shin, Jungwon Woo, and Kwangsoo No

Appl. Phys. Lett. 80, 1453 (2002); http://dx.doi.org/10.1063/1.1454219 (3 pages) | Cited 20 times

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We report on the evidence for the cantilever–sample (CS) capacitive force contribution to the piezoelectric force microscopy (PFM). In addition, we present that positioning of the tip near the edge of the sample surface can significantly reduce this spurious contribution for any combinations of tip cantilever and film. As proof of both the existence of CS interaction and its reduction, the domains formed by the application of voltage pulses through the tip are observed by PFM at two different positions, i.e., sample center and edge. In accordance with the model that a piezoresponse consists of a piezoelectric vibration of the film and an electrostatic force induced vibration of cantilever, the domain contrasts are characterized by dot structure in the amplitude and negligible contrast in the phase images when the tip is placed in the center of the sample surface. However, reducing the CS interaction by placing the tip near the sample edge yields domain contrasts showing ring structure in the amplitude and a clear 180° phase shift in the phase images. Accompanying resolution enhancement in phase images results in smaller size of domains (bits) produced by identical voltage pulses as is evidenced from bit size estimation. Additional evidence for reduction of CS interaction is obtained from piezoresponse hysteresis measurement. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.Dj Domain structure; hysteresis

Picosecond intersubband dynamics in p-Si/SiGe quantum-well emitter structures

P. Murzyn, C. R. Pidgeon, J.-P. R. Wells, I. V. Bradley, Z. Ikonic, R. W. Kelsall, P. Harrison, S. A. Lynch, D. J. Paul, D. D. Arnone, D. J. Robbins, D. Norris, and A. G. Cullis

Appl. Phys. Lett. 80, 1456 (2002); http://dx.doi.org/10.1063/1.1452794 (3 pages) | Cited 23 times

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We report time-resolved (ps) studies of the dynamics of intersubband transitions in p-Si/SiGe multiquantum-well structures in the far-infrared (FIR) regime, ℏω<ℏωLO, utilizing the Dutch free electron laser, (entitled FELIX—free electron laser for infrared radiation). The calculated scattering rates for optic and acoustic phonon, and alloy scattering have been included in a rate equation model of the transient FIR intersubband absorption, and show excellent agreement with our degenerate pump-probe spectroscopy measurements where, after an initial rise time determined by the resolution of our measurement, we determine a decay time of ∼10 ps. This is found to be approximately constant in the temperature range from 4 to 100 K, in good agreement with the predictions of alloy scattering in the Si0.7Ge0.3 wells. © 2002 American Institute of Physics.
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73.21.Fg Quantum wells
78.67.De Quantum wells
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.47.-p Spectroscopy of solid state dynamics
78.30.-j Infrared and Raman spectra
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Potential shielding by the surface water layer in Kelvin probe force microscopy

Hiroyuki Sugimura, Yuzuru Ishida, Kazuyuki Hayashi, Osamu Takai, and Nobuyuki Nakagiri

Appl. Phys. Lett. 80, 1459 (2002); http://dx.doi.org/10.1063/1.1455145 (3 pages) | Cited 60 times

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Kelvin probe force microscopy (KFM) was applied to two-dimensional profiling of silicon pn-structures covered with a 2 nm-thick oxide layer. The surface potential contrast between the p- and n-type regions depended on the hydrophobicity of the oxide surface when KFM imaging was conducted in air with a relative humidity of more than 50%. By decreasing the density of surface hydroxyl groups on the oxide layer through thermal annealing, the potential contrast between the p- and n-type regions increased. While there was no detectable contrast on samples covered with hydrophilic oxide with a water contact angle of almost 0°, contrast increased to greater than 50 mV on the samples covered with hydrophobic oxide with a water contact angle of about 80°. However, when KFM imaging was conducted in a dry nitrogen atmosphere with relative humidity less than 0.6%, a clear potential contrast of about 50 mV could be acquired even on samples covered with the hydrophilic oxide layer. Since samples with less adsorbed water on their surface showed greater potential contrast, contrast degradation is attributed to a shielding effect of the adsorbed water layer. © 2002 American Institute of Physics.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
68.43.Fg Adsorbate structure (binding sites, geometry)
68.03.Cd Surface tension and related phenomena

Performing current versus voltage measurements of single-walled carbon nanotubes using scanning force microscopy

P. J. de Pablo, C. Gómez-Navarro, M. T. Martínez, A. M. Benito, W. K. Maser, J. Colchero, J. Gómez-Herrero, and A. M. Baró

Appl. Phys. Lett. 80, 1462 (2002); http://dx.doi.org/10.1063/1.1453475 (3 pages) | Cited 15 times

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See Also: Erratum

Show Abstract
In this letter, a method is presented to perform current versus voltage measurements on carbon nanotubes using the tip of a scanning force microscope as an electrode that can be positioned along the molecule. This method allows current versus voltage measurements to be carried out at any spot along a nanotube. By using this method, we present indications of ballistic transport in carbon nanotubes, as well as effects in the electrical properties due to the mechanical deformation. This is a general technique that can be applied to any conducting nanowire. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
72.80.Rj Fullerenes and related materials
72.20.Ht High-field and nonlinear effects
68.37.Ps Atomic force microscopy (AFM)
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