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12 Nov 2001

Volume 79, Issue 20, pp. 3215-3366

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Low temperature crystalline Ag–Ni alloy formation from silver and nickel nanoparticles entrapped in a fatty acid composite film

Ashavani Kumar, Chinmay Damle, and Murali Sastry

Appl. Phys. Lett. 79, 3314 (2001); http://dx.doi.org/10.1063/1.1414298 (3 pages) | Cited 5 times

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Nanoparticles of silver and nickel were grown in thermally evaporated fatty acid (stearic acid) films by immersion of the film sequentially in solutions containing Ag+ ions and Ni2+ ions. Attractive electrostatic interaction between the metal cations and the carboxylate ions in the fatty acid film leads to entrapment of the cations in the film. Thereafter, the metal ions were reduced in situ to yield nanoparticles of Ag and Ni of ∼ 30 nm diameter within the fatty acid matrix. Thermal treatment of the stearic acid-(silver+nickel) nanocomposite films led to the formation of a Ni–Ag alloy at ∼ 100 °C. Prolonged heat treatment at this temperature resulted in the phase separation of the alloy and the reformation of individual Ag and Ni nanoparticles. © 2001 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.Fx Diffusion; interface formation
64.75.-g Phase equilibria
81.40.Gh Other heat and thermomechanical treatments
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Formation of ordered Ge quantum dots on the Si(111)–(7×7) surface

Y. P. Zhang, L. Yan, S. S. Xie, S. J. Pang, and H.-J. Gao

Appl. Phys. Lett. 79, 3317 (2001); http://dx.doi.org/10.1063/1.1419052 (3 pages) | Cited 20 times

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We present a pathway for the formation of ordered Ge quantum dots on Si(111)–(7×7) substrate. Self-assembled growth of Ge quantum dots on the Si(111)–(7×7) surface has been investigated using scanning tunneling microscopy. The Ge is grown on the substrate by solid phase epitaxy at room temperature. It has been found that the deposited submonolayer Ge can aggregate and form ordered Ge quantum dots on the surface through controlling the annealing temperature. The formation of ordered Ge quantum dots is due to the preferential adsorption sites of Ge on Si(111)–(7×7). The formed Ge quantum dots may have a great potential in the application of nanodevices. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Cy Elemental semiconductors
81.16.Dn Self-assembly
81.15.Np Solid phase epitaxy; growth from solid phases
68.55.A- Nucleation and growth
61.72.Cc Kinetics of defect formation and annealing
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Excited-state dynamics and carrier capture in InGaAs/GaAs quantum dots

L. Zhang, Thomas F. Boggess, K. Gundogdu, Michael E. Flatté, D. G. Deppe, C. Cao, and O. B. Shchekin

Appl. Phys. Lett. 79, 3320 (2001); http://dx.doi.org/10.1063/1.1418035 (3 pages) | Cited 16 times

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Subpicosecond time-resolved photoluminescence upconversion is used to measure the 12 K first-excited-state dynamics in large InGaAs/GaAs self-assembled quantum dots designed for 1.3 μm diode lasers. A comparison with the ground-state dynamics suggests that energy relaxation occurs in a cascade through the multiple discrete levels with an average interlevel relaxation time of ∼250 fs. Excited-state emission is observed from two distinct populations. Due to the ultrafast relaxation from the excited state to the ground state in dots containing only a single exciton, the excited-state emission is dominated by the fraction of dots that capture more than one electron–hole pair. In this case, state filling in the ground state blocks the ultrafast relaxation channel, thereby enhancing the excited-state emission. While state filling and a random capture process dictate the primary features of the excited-state emission, at low excitation levels we find that the rise time of emission from the excited state is influenced by the much denser population of singly occupied dots. © 2001 American Institute of Physics.
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73.21.La Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
81.07.Ta Quantum dots
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
73.63.Kv Quantum dots
78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Electrode modification by electron-induced patterning of aromatic self-assembled monolayers

T. Felgenhauer, C. Yan, W. Geyer, H.-T. Rong, A. Gölzhäuser, and M. Buck

Appl. Phys. Lett. 79, 3323 (2001); http://dx.doi.org/10.1063/1.1415771 (3 pages) | Cited 25 times

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Self-assembled monolayers of ω-(4′-methyl-biphenyl-4-yl)-dodecyl thiol [CH3–C6H4-C6H4–(CH2)12–SH,BP12] on gold were patterned via exposure to 300 eV electrons. Subsequent copper deposition in an electrochemical cell revealed behavior opposite to that of electron beam patterned monolayers of alkanethiols. Whereas alkanethiols act as a positive resist and lead to copper deposition only on irradiated parts, the biphenyl based thiol acts as a negative resist. At the irradiated areas the layer exhibits blocking behavior and copper deposition is observed only on the nonirradiated parts. © 2001 American Institute of Physics.
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82.45.Mp Thin layers, films, monolayers, membranes
85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Pq Electrodeposition, electroplating
61.80.Fe Electron and positron radiation effects
81.16.Dn Self-assembly
82.45.Qr Electrodeposition and electrodissolution

Controlled creation of a carbon nanotube diode by a scanned gate

Marcus Freitag, Marko Radosavljevic, Yangxin Zhou, A. T. Johnson, and Walter F. Smith

Appl. Phys. Lett. 79, 3326 (2001); http://dx.doi.org/10.1063/1.1419055 (3 pages) | Cited 70 times

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We use scanning gate microscopy to precisely locate the gating response in field-effect transistors (FETs) made from semiconducting single-wall carbon nanotubes. A dramatic increase in transport current occurs when the device is electrostatically doped with holes near the positively biased electrode. We ascribe this behavior to the turn-on of a reverse biased Schottky barrier at the interface between the p-doped nanotube and the electrode. By positioning the gate near one of the contacts, we convert the nanotube FET into a rectifying nanotube diode. These experiments both clarify a longstanding debate over the gating mechanism for nanotube FETs and indicate a strategy for diode fabrication based on controlled placement of acceptor impurities near a contact. © 2001 American Institute of Physics.
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85.35.Kt Nanotube devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.30.Kk Junction diodes
85.30.Tv Field effect devices

Carbon nanotube field-effect inverters

Xiaolei Liu, Chenglung Lee, Chongwu Zhou, and Jie Han

Appl. Phys. Lett. 79, 3329 (2001); http://dx.doi.org/10.1063/1.1417516 (3 pages) | Cited 81 times

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This letter presents p-type metal–oxide–semiconductor (PMOS) and complementary metal–oxide–semiconductor (CMOS) inverters based on single-walled carbon nanotube field-effect transistors. The device structures consist of carbon nanotubes grown via a chemical-vapor deposition method and contacted by two metallic source/drain electrodes. Electrical properties of both p-type (without doping) and n-type nanotube transistors with potassium doping have been measured. By utilizing a resistor as the load for a p-type nanotube field-effect transistor, a PMOS inverter is demonstrated. Furthermore, by connecting a p-type nanotube transistor and an n-type nanotube transistor, a CMOS inverter is demonstrated. Both types of inverters exhibit nice transfer characteristics at room temperature. Our work represents one step forward toward integrated circuits based on nanoelectronic devices. © 2001 American Institute of Physics.
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85.35.Kt Nanotube devices
84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Direct fabrication of two-dimensional titania arrays using interference photolithography

Atsushi Shishido, Ivan B. Diviliansky, I. C. Khoo, Theresa S. Mayer, Suzushi Nishimura, Gina L. Egan, and Thomas E. Mallouk

Appl. Phys. Lett. 79, 3332 (2001); http://dx.doi.org/10.1063/1.1415417 (3 pages) | Cited 27 times

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Two-dimensional (2D) titania arrays with periods of 0.8–2.0 μm were fabricated by polymerization of a photosensitive titanium-containing monomer film using interference photolithography. The 2D precursor arrays were prepared by exposing a mixture of methacrylic acid, ethyleneglycol dimethacrylate, and titanium ethoxide doped with photoinitiator to 355 nm, 15 ns pulses from a Nd-Yttrium–aluminum–garnet laser and then rinsing with methanol. Pure titania arrays were obtained from the precursor arrays by subsequent calcination at 575 °C. The structure of the arrays fabricated by this method was confirmed with optical microscopy and scanning electron microscopy. © 2001 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer

Size-, shape-, and position-controlled GaAs nano-whiskers

B. J. Ohlsson, M. T. Björk, M. H. Magnusson, K. Deppert, L. Samuelson, and L. R. Wallenberg

Appl. Phys. Lett. 79, 3335 (2001); http://dx.doi.org/10.1063/1.1418446 (3 pages) | Cited 115 times

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We have developed a technique for the synthesis of size-selected, GaAs, epitaxial nano-whiskers, grown on a crystalline substrate. As catalysts, we used size-selected gold aerosol particles, which enabled us to fully vary the surface coverage independently of the whisker diameter. The whiskers were rod shaped, with a uniform diameter between 10 and 50 nm, correlated to the size of the catalytic seed. Furthermore, by the use of nano-manipulation of the aerosol particles by means of atomic force microscopy, we can nucleate individual nano-whiskers in a controlled manner at specific positions on a substrate with accuracy on the nm level. © 2001 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
68.37.Ps Atomic force microscopy (AFM)
61.46.-w Structure of nanoscale materials
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
68.55.A- Nucleation and growth

Three-dimensional calculation of field electron energy distributions from open hydrogen-saturated and capped metallic (5,5) carbon nanotubes

A. Mayer, N. M. Miskovsky, and P. H. Cutler

Appl. Phys. Lett. 79, 3338 (2001); http://dx.doi.org/10.1063/1.1418456 (3 pages) | Cited 13 times

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We present three-dimensional simulations of field emission from open and capped (5,5) carbon nanotubes, with consideration of hydrogen saturation of the open structure. The transfer-matrix methodology used for the calculations reproduces appropriate band-structure effects due to the periodic repetition of a basic unit of the nanotubes and the use of Bachelet pseudopotentials. The total-energy distributions of field-emitted electrons contain peaks, which are related to standing waves in the shell of the nanotubes and to resonant states at the apex of the closed structure. These peaks move to lower energies with increasing electric field. The results indicate that field emission is more efficient with the open structure and that hydrogen saturation of the dangling bonds results in a further enhancement of the current.© 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.-w Structure of nanoscale materials
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
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