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16 Jun 2003

Volume 82, Issue 24, pp. 4215-4390

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4322 (2003); http://dx.doi.org/10.1063/1.1582366 (3 pages)

Hongwei Qu, Wei Yao, T. Garcia, Jiandi Zhang, A. V. Sorokin, S. Ducharme, P. A. Dowben, and V. M. Fridkin
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Role of extrinsic atoms on the morphology and field emission properties of carbon nanotubes

L. H. Chan, K. H. Hong, D. Q. Xiao, W. J. Hsieh, S. H. Lai, H. C. Shih, T. C. Lin, F. S. Shieu, K. J. Chen, and H. C. Cheng

Appl. Phys. Lett. 82, 4334 (2003); http://dx.doi.org/10.1063/1.1579136 (3 pages) | Cited 29 times

Online Publication Date: 10 June 2003

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Extrinsic atoms were doped into multiwalled carbon nanotubes (MWCNTs) using microwave plasma-enhanced chemical vapor deposition. Doped nitrogen atoms alter the original parallel graphenes into highly curved ones including some fullerene-like structures. Doped nitrogen atoms could replace carbon atoms in MWCNTs and therefore increase the electronic density that enhances the electron field emission properties. On the other hand, the incorporation of boron into the carbon network apparently increases the concentration of electron holes that become electron traps and eventually impedes the electron field emission properties. Fowler–Nordheim plots show two different slopes in the curve, indicating that the mechanism of field emission is changed from low to high bias voltages. β values could be increased by an amount of 42% under low bias voltages and 60% under high bias voltages in the N-doped MWCNTs, but decreased by an amount of 8% under low bias region and 68% under high bias voltage in the B-doped MWCNTs. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
79.70.+q Field emission, ionization, evaporation, and desorption

Self-embedded nanocrystalline chromium carbides on well-aligned carbon nanotips

C. L. Tsai, J. H. Hsu, and C. F. Chen

Appl. Phys. Lett. 82, 4337 (2003); http://dx.doi.org/10.1063/1.1579867 (3 pages) | Cited 4 times

Online Publication Date: 10 June 2003

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Well-aligned carbon nanotips embedded with nanocrystalline chromium carbide were directly grown on a substrate by microwave plasma chemical vapor deposition. These nanomaterials grew up to about 1 μm long and 60 nm in diameter, yielding a high aspect ratio. In comparison between carbon nanotubes with hollow structure, transmission electron microscopy images show its solid body, which is made of graphite along with nanocrystalline chromium carbide on the tip. These nanomaterials perform well in field emission applications with a turn-on field of 1.38 V/μm and 565 μA/cm2 at 2.2 V/μm. Our result confirms the possibility of the self-embedded nanocrystalline materials on the top of carbon nanotips. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.70.+q Field emission, ionization, evaporation, and desorption
52.77.Dq Plasma-based ion implantation and deposition

II–VI quantum dot formation induced by surface energy change of a strained layer

F. Tinjod, B. Gilles, S. Moehl, K. Kheng, and H. Mariette

Appl. Phys. Lett. 82, 4340 (2003); http://dx.doi.org/10.1063/1.1583141 (3 pages) | Cited 56 times

Online Publication Date: 10 June 2003

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A method for growing self-assembled II–VI quantum dots (QDs) is demonstrated: A highly strained CdTe layer, grown onto Zn(Mg)Te, is covered with an amorphous Te layer which is then desorbed. This induces QD formation, observed as an abrupt change of both the reflection high-energy electron diffraction pattern and the surface morphology studied by atomic force microscopy in an ultrahigh vacuum. The dots are also characterized after capping by microphotoluminescence. This morphology transition, which occurs after and not during the growth, can be understood in terms of variation of the surface energy in presence of the group-VI element, which compensates for the natural trend toward plastic relaxation in II–VI compounds. This method shows the strong influence of the surface energy (and not just the lattice mismatch) in inducing the formation of coherent islands for mismatched systems having a low dislocation formation energy such as CdTe/ZnTe and CdSe/ZnSe. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Dz II-VI semiconductors
68.35.Md Surface thermodynamics, surface energies
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Dn Self-assembly
68.55.-a Thin film structure and morphology

Effect of Si delta doping on the luminescence properties of InP/InAlP quantum dots

X. B. Zhang, R. D. Heller, M. S. Noh, R. D. Dupuis, G. Walter, and N. Holonyak

Appl. Phys. Lett. 82, 4343 (2003); http://dx.doi.org/10.1063/1.1582364 (3 pages) | Cited 7 times

Online Publication Date: 10 June 2003

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We show that the cathodoluminescence (CL) properties of InP quantum dots (QDs) grown on In0.5Al0.5P matrix layers, lattice-matched to (001) GaAs substrates, can be greatly improved by introducing silicon delta doping in the layer adjacent to the QDs. Under optimized conditions, the room-temperature CL intensity of QDs can be improved by ∼ 16 times. We speculate that the increased CL intensity is caused by the efficient capture of electrons from the reservoir of the delta-doped layer into the QDs, which, to some extent, counterbalances the thermal escape of electrons from the QDs. A temperature-dependent CL study of InP QDs grown without Si delta doping shows a quenching of the CL at high temperatures, which supports the unipolar escape of electrons from QDs, while delta-doped QDs show an anomalous behavior. The QD integrated CL intensity increases with temperature and then decreases after 200 K. This anomalous behavior is interpreted as caused by competition between two processes: (1) thermal activation of carriers out of the potential well introduced by delta doping and then capture by QDs, which enhances the CL intensity; and (2) quenching of the CL due to thermal activation of carriers out of the QDs. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.60.Hk Cathodoluminescence, ionoluminescence

Dilute LaB6 nanoparticles in polymer as optimized clear solar control glazing

Stefan Schelm and Geoff B. Smith

Appl. Phys. Lett. 82, 4346 (2003); http://dx.doi.org/10.1063/1.1584092 (3 pages) | Cited 37 times

Online Publication Date: 10 June 2003

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Window samples with a LaB6 nanoparticle-doped polymer laminate were tested for their performances in the reduction of solar heat gain. The near-infrared absorption, caused by the excitation of surface plasmons, was modeled using an average ellipsoid approach, including a size-induced broadening of the Drude part of the dielectric function. The resonance positions are well reproduced by this method and the size effect broadens the bulk resonance to an extent observed in the sample spectra. Additional broadening and spectral features observed in the absorption of the samples are attributed to shape and orientation effects. © 2003 American Institute of Physics.
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42.79.Ek Solar collectors and concentrators
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.-j Infrared and Raman spectra
61.46.-w Structure of nanoscale materials

Controlled self-assembly of semiconductor quantum dots using shadow masks

T. Schallenberg, T. Borzenko, G. Schmidt, M. Obert, G. Bacher, C. Schumacher, G. Karczewski, L. W. Molenkamp, S. Rodt, R. Heitz, and D. Bimberg

Appl. Phys. Lett. 82, 4349 (2003); http://dx.doi.org/10.1063/1.1584511 (3 pages) | Cited 7 times

Online Publication Date: 10 June 2003

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An effective method for controlling the position and number of self-assembled quantum dots (QDs) grown by molecular-beam epitaxy has been developed. Epitaxially grown shadow masks are used to realize selective area growth, which exploits different incidence angles of the molecular beams. We applied this method to control the position and number of self-assembled CdSe QDs in a ZnSe matrix. Bright cathodoluminescence shows the presence of regularly distributed ensembles of QDs and that single QDs can be reliably grown. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.66.Hf II-VI semiconductors
81.07.Ta Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Dz II-VI semiconductors
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Nd Micro- and nanolithography

Fabrication of monodispersive FePt nanoparticle films stabilized on rigid substrates

Andrew C. C. Yu, Mikihisa Mizuno, Yuichi Sasaki, Makoto Inoue, Hirofumi Kondo, Ippei Ohta, David Djayaprawira, and Migaku Takahashi

Appl. Phys. Lett. 82, 4352 (2003); http://dx.doi.org/10.1063/1.1584791 (3 pages) | Cited 33 times

Online Publication Date: 10 June 2003

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Monodispersive FePt nanoparticle films can be stabilized firmly on rigid Si substrates using amino-functional silane, such as [3-(2-aminoethlyamino) propyl]trimethoxysilane, as a coupling layer. The Si substrate/SiO2/APTS/FePt nanoparticles heterostructure was confirmed using high-resolution electron microscopy (HREM). The HREM result agreed well with the x-ray reflectivity measurement upon the individual layer thickness. The as-made superparamagnetic FePt nanoparticle film transformed from chemically disordered fcc structure to chemically ordered L10 phase upon annealing at 800 °C for 30 min under a vacuum of 10−8 Torr. Plan-view high-resolution scanning electron microscopy (HRSEM) observation indicated that under high-vacuum annealing, coalescence of the monodispersive nanoparticle film was not significant. The HRSEM result was consistent with the in-plane x-ray diffractometry measurement, in which sharpening of the diffraction peaks occurred only very slightly for the annealed films. © 2003 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
68.55.-a Thin film structure and morphology
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing

Electron localization by self-assembled GaSb/GaAs quantum dots

M. Hayne, J. Maes, S. Bersier, V. V. Moshchalkov, A. Schliwa, L. Müller-Kirsch, C. Kapteyn, R. Heitz, and D. Bimberg

Appl. Phys. Lett. 82, 4355 (2003); http://dx.doi.org/10.1063/1.1583853 (3 pages) | Cited 19 times

Online Publication Date: 10 June 2003

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We have studied the photoluminescence from type-II GaSb/GaAs self-assembled quantum dots in magnetic fields up to 50 T. Our results show that at low laser power, electrons are more weakly bound to the dots than to the wetting layer, but that at high laser power, the situation is reversed. We attribute this effect to an enhanced Coulomb interaction between a single electron and dots that are multiply charged with holes. © 2003 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Schottky nanocontacts on ZnO nanorod arrays

W. I. Park, Gyu-Chul Yi, J.-W. Kim, and S.-M. Park

Appl. Phys. Lett. 82, 4358 (2003); http://dx.doi.org/10.1063/1.1584089 (3 pages) | Cited 149 times

Online Publication Date: 10 June 2003

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We report on fabrication and electrical characteristics of ZnO nanorod Schottky diode arrays. High quality ZnO nanorods were grown for the fabrication of the Schottky diodes using noncatalytic metalorganic vapor phase epitaxy and Au was evaporated on the tips of the vertically well-aligned ZnO nanorods. I–V characteristics of both bare ZnO and Au/ZnO heterostructure nanorod arrays were measured using current-sensing atomic force microscopy. Although both nanorods exhibited nonlinear and asymmetric I–V characteristic curves, Au/ZnO heterostructure nanorods demonstrated much improved electrical characteristics: the reverse-bias breakdown voltage was improved from −3 to −8 V by capping a Au layer on the nanorod tips. The origin of the enhanced electrical characteristics for the heterostructure nanorods is suggested. © 2003 American Institute of Physics.
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85.35.-p Nanoelectronic devices
85.30.Hi Surface barrier, boundary, and point contact devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.07.Bc Nanocrystalline materials
73.61.Ga II-VI semiconductors
85.30.Kk Junction diodes
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