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27 Oct 2003

Volume 83, Issue 17, pp. 3447-3628

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 3453 (2003); http://dx.doi.org/10.1063/1.1622431 (3 pages)

Giacomo Scalari, Stéphane Blaser, Lassaad Ajili, Jérôme Faist, Harvey Beere, Edmund Linfield, David Ritchie, and Giles Davies
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Instability and dynamics of thin slipping films

Ashutosh Sharma and Kajari Kargupta

Appl. Phys. Lett. 83, 3549 (2003); http://dx.doi.org/10.1063/1.1618376 (3 pages) | Cited 16 times

Online Publication Date: 20 October 2003

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The linear stability analysis of the full Navier–Stokes equations shows that the surface instability and dynamics of thin liquid films are profoundly altered by the presence of slippage on the substrate. For example, the exponents for the length scale (λm∝h0n; h0 is film thickness) and time scale of instability (tr∝h0m) change nonmonotonically with slippage [for van der Waals force induced instability, n ∊ (1.25,2), m ∊ (3,6)]. Slippage always encourages faster rupture and can greatly reduce the number density of holes for moderate to strong slip. Thus, any interpretation of thin film experiments, including determination of intermolecular forces from the length and time scales, needs to account for the possibility of slippage. © 2003 American Institute of Physics.
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68.15.+e Liquid thin films

Enhanced field emission from printed carbon nanotubes by mechanical surface modification

T. J. Vink, M. Gillies, J. C. Kriege, and H. W. J. J. van de Laar

Appl. Phys. Lett. 83, 3552 (2003); http://dx.doi.org/10.1063/1.1622789 (3 pages) | Cited 80 times

Online Publication Date: 20 October 2003

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A method is presented where the morphology of screen printed carbon nanotube pastes is modified using an adhesive tape. In this way, the organic matrix material is preferentially removed leaving an optimal emitter surface of sparsely distributed and well-aligned carbon nanotubes. From these emitter surfaces, homogeneous emission was observed with emitter site densities of at least 104 emitters cm−2 and extracted current densities over 500 mA cm−2. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.07.De Nanotubes
61.46.-w Structure of nanoscale materials

Quantum-dot optical temperature probes

Glen W. Walker, Vikram C. Sundar, Christina M. Rudzinski, Aetna W. Wun, Moungi G. Bawendi, and Daniel G. Nocera

Appl. Phys. Lett. 83, 3555 (2003); http://dx.doi.org/10.1063/1.1620686 (3 pages) | Cited 80 times

Online Publication Date: 20 October 2003

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The steady-state photoluminescence (PL) properties of cadmium selenide quantum dots (QDs) with a zinc sulfide overlayer [(CdSe)ZnS] can be strongly dependent on temperature in the range from 100 to 315 K. The PL intensity from 50 to 55 Å (CdSe)ZnS QDs in poly(lauryl methacrylate) matrices increases by a factor of ∼ 5 when the temperature is decreased from 315 to 100 K, and the peak of the emission band is blueshifted by 20 nm over the same range. The change in PL intensity is appreciable, linear, and reversible (−1.3% per °C) for temperatures close to ambient conditions. These properties of (CdSe)ZnS dots are retained in a variety of matrices including polymer and sol–gel films, and they are independent of excitation wavelength above the band gap. The significant temperature dependence of the luminescence combined with its insensitivity to oxygen quenching establishes (CdSe)ZnS dots as optical temperature indicators for temperature-sensitive coatings. © 2003 American Institute of Physics.
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07.20.Dt Thermometers
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors

Effect of germanium concentration and tunnel oxide thickness on nanocrystal formation and charge storage/retention characteristics of a trilayer memory structure

V. Ho, L. W. Teo, W. K. Choi, W. K. Chim, M. S. Tay, D. A. Antoniadis, E. A. Fitzgerald, A. Y. Du, C. H. Tung, R. Liu, and A. T. S. Wee

Appl. Phys. Lett. 83, 3558 (2003); http://dx.doi.org/10.1063/1.1615840 (3 pages) | Cited 13 times

Online Publication Date: 20 October 2003

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The effect of germanium concentration and the rapid thermal oxide (RTO) layer thickness on the nanocrystal formation and charge storage/retention capability of a trilayer metal–insulator–semiconductor device was studied. We found that the RTO and the capping oxide layers were not totally effective in confining the Ge nanocrystals in the middle layer when a pure Ge middle layer was used for the formation of nanocrystals. From the transmission electron microscopy and secondary ion mass spectroscopy results, a significant diffusion of Ge atoms through the RTO and into the silicon substrate was observed when the RTO layer thickness was reduced to 2.5 nm. This resulted in no (or very few) nanocrystals formed in the system. For devices with a Ge+SiO2 cosputtered middle layer (i.e., lower Ge concentration), even though a higher charge storage capability was obtained from devices with a thinner RTO layer, the charge retention capability was poorer as compared to devices with a thicker RTO layer. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.46.-w Structure of nanoscale materials

Structure and growth of monoclinic Mo2S3 nanorods

R. C. Che, N. Bai, and L.-M. Peng

Appl. Phys. Lett. 83, 3561 (2003); http://dx.doi.org/10.1063/1.1623005 (3 pages) | Cited 3 times

Online Publication Date: 20 October 2003

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We report the synthesis of sulfide nanostructures with trivalent molybdenum, i.e., crystalline Mo2S3 nanorods via a solid-gas reaction between porous Al2O3 impregnated with MoO3 and H2S gas. We show that the introduction of additional 8% H2 gas results in MoS2 nanotubes of the same size. A growth model is proposed for the formation of Mo2S3 nanorods, and the effect of H2 is discussed and demonstrated. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.10.Bk Growth from vapor

Photoinduced conductivity changes in carbon nanotube transistors

Moonsub Shim and Giles P. Siddons

Appl. Phys. Lett. 83, 3564 (2003); http://dx.doi.org/10.1063/1.1622450 (3 pages) | Cited 30 times

Online Publication Date: 20 October 2003

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Photoinduced conductivity changes in single-walled carbon nanotube transistors have been examined. Low-intensity ultraviolet light significantly reduces the p-channel conductance while simultaneously increasing the n-channel conductance. A combination of optical absorption and electron transport measurements reveals that these changes occur without variations in dopant concentrations. Possible sites of oxygen photodesorption and its implications on the observed electronic properties of nanotubes are considered. © 2003 American Institute of Physics.
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85.35.Kt Nanotube devices
73.63.Fg Nanotubes
85.30.Tv Field effect devices
68.43.Tj Photon stimulated desorption
79.20.La Photon- and electron-stimulated desorption

Determination of carrier density in Te-doped Bi nanowires

Yu-Ming Lin and M. S. Dresselhaus

Appl. Phys. Lett. 83, 3567 (2003); http://dx.doi.org/10.1063/1.1614443 (3 pages) | Cited 4 times

Online Publication Date: 20 October 2003

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A promising approach is presented to characterize the carrier density in Te-doped Bi nanowires from their temperature-dependent resistance measurements, based on the comparison of the scattering rates due to charged impurity scattering and due to other scattering mechanisms that are independent of the carrier density. The result shows that the Te doping efficiency δe is only about 10%–15% for Te-doped Bi nanowires synthesized in an alumina template by molten-metal pressure injection. This analysis technique can be extended to other nanowire systems to provide valuable information regarding the carrier concentration and the Fermi energy for use in controlling and optimizing nanowire properties for specific applications. © 2003 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Cw Elemental semiconductors
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Binding energy of parallel carbon nanotubes

B. Chen, M. Gao, J. M. Zuo, S. Qu, B. Liu, and Y. Huang

Appl. Phys. Lett. 83, 3570 (2003); http://dx.doi.org/10.1063/1.1623013 (2 pages) | Cited 29 times

Online Publication Date: 20 October 2003

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We study the interaction between two separate carbon nanotubes that bond together by examing their geometry in transmission electron microscopy (TEM). The TEM image, in conjunction with a continuum mechanics model interpretation, provides an estimate of 0.36 nN binding energy between the two parallel carbon nanotubes. This result agrees well with the calculated binding energy using an atomistic model. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
68.37.Lp Transmission electron microscopy (TEM)
73.22.-f Electronic structure of nanoscale materials and related systems
61.50.Lt Crystal binding; cohesive energy
71.15.Nc Total energy and cohesive energy calculations

Ultrafast intraband spectroscopy of electron capture and relaxation in InAs/GaAs quantum dots

T. Müller, F. F. Schrey, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 83, 3572 (2003); http://dx.doi.org/10.1063/1.1622432 (3 pages) | Cited 42 times

Online Publication Date: 20 October 2003

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The electron capture and relaxation dynamics in self-assembled InAs/GaAs quantum dots (QDs) is investigated by means of interband-pump–intraband-probe spectroscopy. By tuning femtosecond infrared pulses into resonance with intraband transitions between confined QD states and the wetting layer continuum, the electron population of the QD ground and first excited states is determined as a function of time delay after the interband pump. Our experiments indicate that the most efficient relaxation pathway into the QD ground state is the stepwise relaxation through the excited states of the dot. The capture time at room temperature decreases from 2.8 to 1.5 ps with increasing excitation density above a certain threshold, and changes only slightly at low excitation densities. At low temperature (T = 5 K), we determine a longer capture time of 4.7 ps. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.47.-p Spectroscopy of solid state dynamics
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors

Tuning the properties of magnetic CdMnTe quantum dots

S. Mackowski, H. E. Jackson, L. M. Smith, J. Kossut, G. Karczewski, and W. Heiss

Appl. Phys. Lett. 83, 3575 (2003); http://dx.doi.org/10.1063/1.1622438 (3 pages) | Cited 21 times

Online Publication Date: 20 October 2003

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We show that CdMnTe self-assembled quantum dots (QDs) can be formed by depositing a submonolayer of Mn ions over a ZnTe surface prior to deposition of the CdTe dot layer. Single-dot emission lines and strongly polarized QD photoluminescence (PL) in an applied magnetic field confirm the presence of Mn in individual QDs. The width of PL lines of the single CdMnTe dots is 3 meV due to magnetic moment fluctuations (MMFs) of the Mn ions. After rapid thermal annealing, the emission lines of individual magnetic QDs narrow significantly to 0.25 meV, showing that effect of MMFs is strongly reduced, most probably due to an increase in the average QD size. These results suggest a way to tune the spin properties of magnetic QDs. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
73.63.Kv Quantum dots
73.21.La Quantum dots
75.50.Pp Magnetic semiconductors
75.75.-c Magnetic properties of nanostructures
78.55.Et II-VI semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities

Thermal emission of electrons from selected s-shell configurations in InAs/GaAs quantum dots

O. Engström, M. Malmkvist, Y. Fu, H. Ö. Olafsson, and E. Ö. Sveinbjörnsson

Appl. Phys. Lett. 83, 3578 (2003); http://dx.doi.org/10.1063/1.1622437 (3 pages) | Cited 27 times

Online Publication Date: 20 October 2003

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The thermal emission of electrons from self-assembled InAs/GaAs quantum dots, prepared by molecular-beam epitaxy, with an average base/height size of 20 nm/11 nm in Schottky diodes has been investigated using deep level transient spectroscopy (DLTS). By applying an appropriate set of voltage pulses across the Schottky diode, the two different s-electron configurations have been investigated separately. This avoids the problem of interference between overlapping peaks in DLTS data. We find that a difference in activation energy for the thermal electron emission between the two configurations agrees with expected variation in electron energy levels due to the size distribution of the quantum dots. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.63.Kv Quantum dots
73.21.La Quantum dots

Tailoring structure and electrical properties of carbon nanotubes using kilo-electron-volt ions

B. Q. Wei, J. D’Arcy-Gall, P. M. Ajayan, and G. Ramanath

Appl. Phys. Lett. 83, 3581 (2003); http://dx.doi.org/10.1063/1.1622781 (3 pages) | Cited 32 times

Online Publication Date: 20 October 2003

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We report the effects of 30 and 50 keV Ga+ ion irradiation on the structure and electrical properties of arc-evaporated multiwalled carbon nanotubes (MWNTs). For 50 keV ions with doses of ∼ 1013 ions/cm2 the outer shells of the MWNTs remain intact, while the inner layers reorganize into highly ordered pillbox-like ∼5-nm-diam nanocompartments of varying lengths between 2 and 20 nm. Increasing the dose to ∼ 1014 ions cm−2 results in the gradual disordering of the graphitic shells and destroys the nanocapsules, while at doses of 1015 ions cm−2 the graphitic shells collapse into the hollow, resulting in the formation a homogenous amorphous rod. Irradiating nanotubes with 30 keV ions yields similar results, but at higher doses. Irradiated nanotubes exhibit a decrease in electron activation energy from 194 to 112 meV, while the semiconducting behavior is essentially preserved for ion doses up to 5×1015 ions cm−2. Ion irradiation could be a useful tool to locally modify nanotube structure and tailor properties for device applications. © 2003 American Institute of Physics.
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73.63.Fg Nanotubes
61.46.-w Structure of nanoscale materials
61.80.Jh Ion radiation effects
81.07.De Nanotubes
61.82.Fk Semiconductors

Synthesis, structure, and photoluminescence of very thin and wide alpha silicon nitride (α-Si3N4) single-crystalline nanobelts

Long-Wei Yin, Yoshio Bando, Ying-Chun Zhu, and Yu-Bao Li

Appl. Phys. Lett. 83, 3584 (2003); http://dx.doi.org/10.1063/1.1623940 (3 pages) | Cited 42 times

Online Publication Date: 20 October 2003

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Large quantities of very thin and wide single-crystal alpha silicon nitride (α-Si3N4) nanobelts were synthesized by a vapor-solid thermal reaction between ammonia and silicon monoxide (SiO) without using any added catalyst. Scanning electron microscopy, high-resolution electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction were used to characterize the formed nanobelts. The single-crystal α-Si3N4 nanobelts are about 800–1200 nm in width, 20–35 nm in thickness and about several tens to several hundreds of micrometers in length. The nanobelts are perfect in structure. The nanobelts grow along [011] and [100] direction. Intense visible photoluminescence (PL) occurring on the wide and thin nanobelts over a broad spectrum ranging from 420 to 750 nm was observed. The visible PL emission is related to the inherently imperfect Si and N dangling bonds in the α-Si3N4 structure. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
78.55.Hx Other solid inorganic materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Local anisotropy in strained manganite thin films

N. M. Souza-Neto, A. Y. Ramos, H. C. N. Tolentino, E. Favre-Nicolin, and L. Ranno

Appl. Phys. Lett. 83, 3587 (2003); http://dx.doi.org/10.1063/1.1623936 (3 pages) | Cited 2 times

Online Publication Date: 20 October 2003

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We report on an angular resolved x-ray absorption spectroscopy study of the local atomic structure around the manganese ions in La0.7Sr0.3MnO3 thin films epitaxially grown on tensile and compressive substrates. Ab initio calculations provide strong support to the analysis of the experimental data and make possible the unambiguous derivation of a model of local distortion around the manganese atoms, without modification of the tilt angle Mn–O–Mn, among the octahedra. This distortion, tending to localize the charge carriers, is the driving parameter in the modifications of the magnetic and transport properties observed in thin films with respect to bulk systems. © 2003 American Institute of Physics.
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78.70.Dm X-ray absorption spectra
68.55.-a Thin film structure and morphology
61.66.Fn Inorganic compounds
68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Titanium metal quantum-dot composite induced by subplantation

J. P. Zhao, D. X. Huang, A. J. Jacobson, and J. W. Rabalais

Appl. Phys. Lett. 83, 3590 (2003); http://dx.doi.org/10.1063/1.1622784 (3 pages) | Cited 4 times

Online Publication Date: 20 October 2003

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Crystalline titanium nanodots have been formed in the subsurface layer of single-crystal SiO2, i.e., a Ti-based metal quantum dot composite, by subplantation of 9 keV Ti+ ions. Transmission electron microscopy images show that the Ti nanodots have a single, uniform size distribution of ∼3–4 nm, they are single crystals of mainly the Ti bcc β-phase, and their position in the subsurface is controllable through the ion energy. The unique features of subplantation for promoting the precipitation/clustering of crystalline Ti nanodots are discussed. These results confirm previous findings based on the linear optical properties of Ti in SiO2. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Ta Quantum dots
78.67.Hc Quantum dots
61.46.-w Structure of nanoscale materials
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.37.Lp Transmission electron microscopy (TEM)
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation

Selective formation of ZnO nanodots on nanopatterned substrates by metalorganic chemical vapor deposition

Sang-Woo Kim, Teruhisa Kotani, Masaya Ueda, Shizuo Fujita, and Shigeo Fujita

Appl. Phys. Lett. 83, 3593 (2003); http://dx.doi.org/10.1063/1.1622795 (3 pages) | Cited 15 times

Online Publication Date: 20 October 2003

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Selective formation of ZnO nanodots was accomplished by metalorganic chemical vapor deposition on nanopatterned SiO2/Si substrates. Self-organized ZnO nanodots were selectively formed in nanopatterned lines of Si created by etching of SiO2 with focused ion beam (FIB), whereas any nanodots were hardly observed on the SiO2 surface in the vicinity of the FIB-sputtered Si areas. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned lines is mainly attributed to the effective migration of Zn adatoms diffusing on the SiO2 surface into the Si lines followed by the nucleation at surface atomic steps and kinks created by Ga+ ion sputtering. Cathodoluminescence measurements confirmed that the emission originated from the selectively grown ZnO nanodots. © 2003 American Institute of Physics.
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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.)
81.05.Dz II-VI semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
68.35.Fx Diffusion; interface formation
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