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25 Jun 2007

Volume 90, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 90, 262501 (2007); http://dx.doi.org/10.1063/1.2752015 (3 pages)

Ian Appelbaum and Douwe J. Monsma
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Investigation of the chemical composition profile of SiGe/Si(001) islands by analytical transmission electron microscopy

M. Schade, F. Heyroth, F. Syrowatka, H. S. Leipner, T. Boeck, and M. Hanke

Appl. Phys. Lett. 90, 263101 (2007); http://dx.doi.org/10.1063/1.2751598 (3 pages) | Cited 2 times

Online Publication Date: 25 June 2007

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The authors have determined the composition profile within individual Si1−xGex nanoscale islands on Si(001). Samples have been grown by means of liquid phase epitaxy in the Stranski-Krastanov mode. By applying electron energy loss spectroscopy, the intensities of Si K and Ge L edges have been measured to determine the relative atomic concentration of germanium. The quantification of the composition suggests a profile comprising of two regions with different linear concentration gradients.
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82.80.-d Chemical analysis and related physical methods of analysis
68.47.Fg Semiconductor surfaces
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
79.20.Uv Electron energy loss spectroscopy

Microstructural stability of nanocrystalline LiCoO2 in lithium thin-film batteries under high-voltage cycling

Chiung-Nan Li, Jenn-Ming Yang, Victor Krasnov, Jeff Arias, and Kai-Wei Nieh

Appl. Phys. Lett. 90, 263102 (2007); http://dx.doi.org/10.1063/1.2751609 (3 pages) | Cited 4 times

Online Publication Date: 25 June 2007

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The microstructural stability of nanocrystalline LiCoO2 cathodes in rechargeable thin-film batteries after high-voltage cycling was investigated by transmission electron microscopy. It was found that besides the trigonal-LiCoO2 phase, there are two other phases of LixCoO2, spinel and H1–3, that form inside the nanocrystalline cathode after electrochemical cycling (charge cutoff voltages ≧4.5 V). The formation of the aforementioned secondary phases in the cathode material is irreversible and leads to capacity loss in lithium thin-film batteries.
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82.47.Aa Lithium-ion batteries
82.45.Fk Electrodes

Properties of B and P doped Ge nanowires

H. Peelaers, B. Partoens, and F. M. Peeters

Appl. Phys. Lett. 90, 263103 (2007); http://dx.doi.org/10.1063/1.2752107 (3 pages) | Cited 18 times

Online Publication Date: 25 June 2007

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An ab initio study of the formation and segregation energies of B and P doped Ge nanowires oriented along the [110] direction is performed for fully relaxed H-passivated nanowires. The authors found the preferential dopant positions and the associated formation energies. Edge positions are favorable positions for both types of dopants. In the presence of dangling bond defects P dopants will highly favor the edge positions near the dangling bond, thereby trapping the additional carrier. The results are compared with those found for doped Si nanowires.
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71.55.Cn Elemental semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

ZnO nanoparticle growth on single-walled carbon nanotubes by atomic layer deposition and a consequent lifetime elongation of nanotube field emission

Yo-Sep Min, Eun Ju Bae, Jong Bong Park, Un Jeong Kim, Wanjun Park, Jaewon Song, Cheol Seong Hwang, and Noejung Park

Appl. Phys. Lett. 90, 263104 (2007); http://dx.doi.org/10.1063/1.2745226 (3 pages) | Cited 13 times

Online Publication Date: 25 June 2007

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ZnO nanoparticles were grown on single-walled carbon nanotubes (SWNTs) by atomic layer deposition using diethylzinc (DEZ) and water. The athors discuss that, because of chemical inertness of nanotubes to DEZ and water molecules, such nanoparticles are not likely to grow on the wall of clean and perfect nanotubes. Rather, the growth of ZnO nanoparticles should be attributed to imperfection of nanotubes, such as defects and carbonaceous impurities. Lifetime of field emission from SWNTs with the ZnO nanoparticles is 2.5 times longer than that from the as-grown nanotubes. It is thought that the protection of the defects or impurities by ZnO nanoparticles mainly contributed to the improvement of the field emission lifetime from SWNTs.
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81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
79.70.+q Field emission, ionization, evaporation, and desorption
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.)

Effect of interface scattering on phonon thermal conductivity percolation in random nanowire composites

Weixue Tian and Ronggui Yang

Appl. Phys. Lett. 90, 263105 (2007); http://dx.doi.org/10.1063/1.2751610 (3 pages) | Cited 17 times

Online Publication Date: 26 June 2007

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The effect of phonon-interface scattering on the percolation of the phonon thermal conductivity in random nanowire composites is investigated by solving the phonon Boltzmann transport equation using the Monte Carlo simulation. The forming of a geometric percolating network does not lead to dramatic increase of the thermal conductivity in nanowire composites because of the dominance of the phonon-interface scattering. The thermal conductivity of nanocomposites is much less sensitive to the thermal conductivity contrast ratios of the constituent materials than that of bulk composites, especially when the volumetric concentration of the high thermal conductivity constituent is below the percolation threshold.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Enhanced photoluminescence of ZnO/Er2O3 core-shell structure nanorods synthesized by pulsed laser deposition

S. Z. Li, C. L. Gan, H. Cai, C. L. Yuan, J. Guo, P. S. Lee, and J. Ma

Appl. Phys. Lett. 90, 263106 (2007); http://dx.doi.org/10.1063/1.2752020 (3 pages) | Cited 15 times

Online Publication Date: 26 June 2007

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A narrow size distribution of ZnO nanorod array has been synthesized on silicon substrate by pulsed laser deposition (PLD) in argon ambient. ZnO/Er2O3 core-shell nanostructures were then formed through PLD of a thin Er2O3 layer onto the fabricated ZnO nanorod surface. Transmission electron microscopy analysis shows that both the ZnO core and Er2O3 shell are polycrystalline. Photoluminescence measurement was carried out to characterize the optical properties of the core-shell nanostructures. The band diagram of the core-shell structure shows that a type-II nanostructure may have formed, which explains the ultraviolet emission enhancement of the core-shell structure over pure ZnO nanorods.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.-m Photoluminescence, properties and materials
61.46.-w Structure of nanoscale materials
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Interfaces in semiconductor/metal radial superlattices

Christoph Deneke, Wilfried Sigle, Ulrike Eigenthaler, Peter A. van Aken, Gisela Schütz, and Oliver G. Schmidt

Appl. Phys. Lett. 90, 263107 (2007); http://dx.doi.org/10.1063/1.2742323 (3 pages) | Cited 17 times

Online Publication Date: 26 June 2007

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Semiconductor/metal radial superlattices are produced by the roll-up of inherently strained InGaAs/Ti/Au as well as InAlGaAs/GaAs/Cr films. Cross sections of the obtained structures are prepared and investigated in detail by diverse transmission electron microscopy as well as microanalysis techniques. Special attention is paid to the interfaces of the semiconductor/metal hybrid superlattice. The study reveals amorphous, noncrystalline layers for the semiconductor/metal as well as for the metal/semiconductor interface. The chemical analysis suggests that the observed interlayers are oxides giving rise to a semiconductor/oxide/metal/oxide superlattice rather than a pure semiconductor/metal superlattice.
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68.65.Cd Superlattices
68.35.Ct Interface structure and roughness
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
79.20.Uv Electron energy loss spectroscopy

Tunable electrical conductivity in nanoscale Gd-doped ceria thin films

Annamalai Karthikeyan, Masaru Tsuchiya, Chia-Lin Chang, and Shriram Ramanathan

Appl. Phys. Lett. 90, 263108 (2007); http://dx.doi.org/10.1063/1.2752028 (3 pages) | Cited 10 times

Online Publication Date: 26 June 2007

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Nanoscale Gd-doped ceria thin films exhibit a slow change in conductivity upon high temperature (>800 °C) annealing for extended period of time in controlled oxygen environments. Conductivity can be modulated reversibly upon thermochemical conditioning. The process is kinetically driven, and hence transient states can be quenched at lower temperatures. Nanoscale oxides with more than one order of difference in electrical properties can be obtained by suitable treatments. The results are of potential relevance to synthesizing oxides with controlled functional properties.
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73.61.-r Electrical properties of specific thin films
73.63.-b Electronic transport in nanoscale materials and structures
81.40.Gh Other heat and thermomechanical treatments
72.60.+g Mixed conductivity and conductivity transitions
66.30.H- Self-diffusion and ionic conduction in nonmetals

Growth mechanisms of amorphous SiOx nanowires

Igor Aharonovich, Yeshayahu Lifshitz, and Shoshana Tamir

Appl. Phys. Lett. 90, 263109 (2007); http://dx.doi.org/10.1063/1.2748101 (3 pages) | Cited 10 times

Online Publication Date: 26 June 2007

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Amorphous SiOx nanowires (NWs) 10–50 nm thick and tens of microns long were grown by laser ablation of silicon containing targets onto different substrates held at elevated temperatures. The influence of the growth parameters on the NWs growth and structure was studied. Deposition of a metal catalyst on the substrates was found essential for the SiOx NW growth. The morphology and structure of the NWs were studied using high resolution scanning and transmission electron microscopes with their accessories. Possible growth mechanisms of these nanowires were suggested and discussed.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
61.43.Er Other amorphous solids
81.16.Hc Catalytic methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Formation of a one-dimensional grating at the molecular scale by self-assembly of straight silicon nanowires

H. Sahaf, L. Masson, C. Léandri, B. Aufray, G. Le Lay, and F. Ronci

Appl. Phys. Lett. 90, 263110 (2007); http://dx.doi.org/10.1063/1.2752125 (3 pages) | Cited 21 times

Online Publication Date: 26 June 2007

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Upon submonolayer deposition of silicon onto the anisotropic silver (110) surface flat lying individual Si nanowires, all oriented along the [−110] direction, can be grown at room temperature with a high aspect ratio. Upon deposition at ∼ 200 °C, these one-dimensional nanostructures self-assemble by lateral compaction to form a regular array of essentially identical nanowires, ∼ 1.6 nm in width, covering uniformly the entire substrate surface. They realize, at macroscopic sizes, a highly perfect one-dimensional grating with a molecular-scale pitch of just 2 nm.
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81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Dn Self-assembly
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials

Nuclear magnetic resonance force microscopy with a microwire rf source

M. Poggio, C. L. Degen, C. T. Rettner, H. J. Mamin, and D. Rugar

Appl. Phys. Lett. 90, 263111 (2007); http://dx.doi.org/10.1063/1.2752536 (3 pages) | Cited 13 times

Online Publication Date: 26 June 2007

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The authors use a 1.0 μm wide patterned Cu wire with an integrated nanomagnetic tip to measure the statistical nuclear polarization of 19F in CaF2 by magnetic resonance force microscopy. With less than 350 μW of dissipated power, the authors achieve rf magnetic fields over 4 mT at 115 MHz for a sample positioned within 100 nm of the “microwire” rf source. A 200 nm diameter FeCo tip integrated onto the wire produces field gradients greater than 105 T/m at the same position. The large rf fields from the broadband microwire enable long rotating-frame spin lifetimes of up to 15 s at 4 K.
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61.05.Qr Magnetic resonance techniques; Mössbauer spectroscopy (for structure determination only)
68.37.Rt Magnetic force microscopy (MFM)
76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization

Photoluminescence spectroscopy of bioconjugated CdSe/ZnS quantum dots

M. Dybiec, G. Chornokur, S. Ostapenko, A. Wolcott, J. Z. Zhang, A. Zajac, C. Phelan, T. Sellers, and D. Gerion

Appl. Phys. Lett. 90, 263112 (2007); http://dx.doi.org/10.1063/1.2752537 (3 pages) | Cited 23 times

Online Publication Date: 26 June 2007

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The authors performed scanning photoluminescence (PL) spectroscopy on CdSe/ZnS core/shell quantum dots (QDs) bioconjugated to Interleukin 10 (IL10) antibody. The influence of IL10 on the QD photoluminescence spectra was explored on samples dried on solid substrates at various temperatures. A “blue” up to 15 nm spectral shift of the PL maximum was observed on the bioconjugated QDs. The spectral shift is strongly increased after samples annealing above room temperature. A mechanism of the observed effect is attributed to changes in the QD electronic energy levels caused by local electric or stress field or chemical reactions which occurred on the QD surface.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
87.14.E- Proteins

Study on the quantum confinement effect on ultraviolet photoluminescence of crystalline ZnO nanoparticles with nearly uniform size

Z. D. Fu, Y. S. Cui, S. Y. Zhang, J. Chen, D. P. Yu, S. L. Zhang, L. Niu, and J. Z. Jiang

Appl. Phys. Lett. 90, 263113 (2007); http://dx.doi.org/10.1063/1.2750527 (3 pages) | Cited 18 times

Online Publication Date: 27 June 2007

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Crystalline ZnO nanoparticles with nearly uniform size were studied using photoluminescence and Raman spectroscopy. The main spectral feature of ultraviolet photoluminescence is attributed to the recombination of free exciton (FX) and the first surface phonon replica of FX emission. The energy of FX emission shows a clear blueshift as the size of nanoparticles decreases, indicating that the quantum confinement effect exists in the electronic structure of nano-ZnO, although no confinement effect on the vibrational modes has been found in the same series of samples.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
68.35.Ja Surface and interface dynamics and vibrations

Observation of the negative differential capacitance in Schottky diodes with InAs quantum dots near room temperature

S. D. Lin, V. V. Ilchenko, V. V. Marin, N. V. Shkil, A. A. Buyanin, K. Y. Panarin, and O. V. Tretyak

Appl. Phys. Lett. 90, 263114 (2007); http://dx.doi.org/10.1063/1.2752737 (3 pages) | Cited 6 times

Online Publication Date: 27 June 2007

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The negative differential capacitance (NDC) of Schottky diodes with the layers of InAs quantum dots (QDs) has been clearly observed near room temperature. A simple model involving two zero-dimensional quantum states is proposed to explain the NDC behavior. The simulation results show that the NDC is caused by the fast charging-discharging process in the second states of QDs.
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85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.De Semiconductor-device characterization, design, and modeling

Enhanced radiation tolerance in nanocrystalline MgGa2O4

Tong D. Shen, Shihai Feng, Ming Tang, James A. Valdez, Yongqiang Wang, and Kurt E. Sickafus

Appl. Phys. Lett. 90, 263115 (2007); http://dx.doi.org/10.1063/1.2753098 (3 pages) | Cited 35 times

Online Publication Date: 29 June 2007

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The authors demonstrate a substantial enhancement in radiation-induced amorphization resistance for single-phased nanocrystalline (NC) versus large-grained polycrystalline MgGa2O4. NC and large-grained MgGa2O4 were irradiated at ∼ 100 K with 300 keV Kr++ ions to fluences ranging between 5×1019 and 4×1020 Kr/m2. Large-grained MgGa2O4 samples began to amorphize by a fluence of 5×1019 Kr/m2, while NC MgGa2O4 remained crystalline with no evidence for structural changes (other than moderate grain growth in the lowermost implanted region), to a fluence of 4×1020 Kr/m2. To our knowledge, this is the first experimental study to reveal enhanced amorphization resistance in an irradiated, single-phase, NC material.
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61.80.Jh Ion radiation effects
61.82.Rx Nanocrystalline materials
61.46.Hk Nanocrystals
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