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9 Dec 2002

Volume 81, Issue 24, pp. 4499-4663

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Simple catalyst for the growth of small-diameter carbon nanotubes

P. M. Campbell, E. S. Snow, and J. P. Novak

Appl. Phys. Lett. 81, 4586 (2002); http://dx.doi.org/10.1063/1.1528735 (3 pages) | Cited 14 times

Online Publication Date: 3 December 2002

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We describe a simple technique to grow small (approximately 1–4 nm) diam carbon nanotubes both in and out of the plane of a silicon substrate using the decomposition of ethylene and a nickel–iron thin film catalyst. This procedure can be used to produce nanotubes for ultrasharp atomic force microscope probes as well as for nanotube-based electronic devices. The technique is compatible with the patterned growth of nanotubes and with standard device microfabrication processes. © 2002 American Institute of Physics.
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81.07.De Nanotubes
81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
68.37.Ps Atomic force microscopy (AFM)

Single-electron tunneling to insulator surfaces detected by electrostatic force

L. J. Klein and C. C. Williams

Appl. Phys. Lett. 81, 4589 (2002); http://dx.doi.org/10.1063/1.1525886 (3 pages) | Cited 17 times

Online Publication Date: 3 December 2002

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The detection of single-electron tunneling events between a metallic scanning probe tip and an insulating surface is demonstrated by an electrostatic force method. When a voltage-biased oscillating atomic force microscopy tip is placed within tunneling range of the surface of an insulator, single-electron tunneling events are observed between the tip and electronic states at the surface. The events cause an abrupt reduction in cantilever oscillation amplitude, due to the instantaneous reduction of the force gradient at the tip. In most cases, only a single electron tunnels to or from the surface. Experimental data show that no physical contact is made during the tunneling events. © 2002 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Ns Metal-nonmetal contacts
73.40.Gk Tunneling
73.20.At Surface states, band structure, electron density of states
85.35.Gv Single electron devices

Synthesis and magnetic behavior of an array of nickel-filled carbon nanotubes

Jianchun Bao, Quanfa Zhou, Jianming Hong, and Zheng Xu

Appl. Phys. Lett. 81, 4592 (2002); http://dx.doi.org/10.1063/1.1526461 (3 pages) | Cited 35 times

Online Publication Date: 3 December 2002

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Highly-ordered arrays of Ni-filled carbon nanotubes have been fabricated by a second-order template method. First, an array of aligned carbon nanotubes was generated in a porous alumina membrane by catalytic pyrolysis of acetylene. The desired material, such as nickel, was then filled into the aligned carbon nanotubes by electrodeposition. The remarkable features of this method are: (i) high yield of metal-filled carbon nanotubes, and (ii) the wall thickness of the carbon nanotubes, and the length, diameter, and structure of the metal nanowires in the carbon nanotubes are controllable via changing experimental conditions. This method should be applicable for preparation of other metal- and alloy-filled carbon nanotubes, and allow the reliable technological application in nanoelectronic devices, high-density magnetic memories, electrochemical energy storages and sensors, etc. © 2002 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
75.50.Tt Fine-particle systems; nanocrystalline materials

Single-electron transistors and memory cells with Au colloidal islands

C. S. Wu, C. D. Chen, S. M. Shih, and W. F. Su

Appl. Phys. Lett. 81, 4595 (2002); http://dx.doi.org/10.1063/1.1527236 (3 pages) | Cited 12 times

Online Publication Date: 3 December 2002

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In this study, single-electron transistors and memory cells with Au colloidal islands linked by C60 derivatives have been fabricated by hybridization of top–down advanced electron-beam lithography and bottom–up nanophased-material synthesis techniques. Low-temperature transport measurements exhibit clear Coulomb-blockade-type current–voltage characteristics and hysteretic-type gate-modulated current. The hysteresis is attributed to the presence of electrically isolated charge–storage islands. With the guidance provided by Monte Carlo simulation, we propose a circuit model and give an estimate of the sample parameters. © 2002 American Institute of Physics.
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85.35.Gv Single electron devices
85.65.+h Molecular electronic devices
85.40.Hp Lithography, masks and pattern transfer
85.30.De Semiconductor-device characterization, design, and modeling
81.16.Be Chemical synthesis methods

Magnetic properties and magnetoresistance in small iron oxide cluster assemblies

D. L. Peng, T. Asai, N. Nozawa, T. Hihara, and K. Sumiyama

Appl. Phys. Lett. 81, 4598 (2002); http://dx.doi.org/10.1063/1.1528725 (3 pages) | Cited 25 times

Online Publication Date: 3 December 2002

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We report the magnetic properties and magnetoresistance (MR) in small iron oxide (Fe3−xO4 and Fe3O4) cluster assemblies. Half-metallic Fe3O4 cluster assembly with grain size of 10–15 nm is shown to exhibit a MR value of about 8% at T = 30 K and a peak around the Verwey transition temperature Tv = 115 K which is a little lower than the Tv value ( ∼ 120 K) of single crystal specimens. Even at T = 5 K, the magnetization is not saturated in fields up to 50 kOe. The MR behaviors of a Fe3−xO4-coated iron cluster assembly and a sample which was prepared by embedding the Fe3−xO4-coated iron clusters into a MgO matrix are also studied for comparison. The MR value of the latter is over one time larger than that of the former and is also larger than those of the Fe3O4 cluster assembly at various temperatures. It suggests that the barrier layer is important for enhancing the MR effect at high temperatures. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.60.+g Mixed conductivity and conductivity transitions

Retardation of oxidation in Co nanocolumns: Scanning tunneling microscopy study

J. P. Singh, G.-R. Yang, T.-M. Lu, and G.-C. Wang

Appl. Phys. Lett. 81, 4601 (2002); http://dx.doi.org/10.1063/1.1527980 (3 pages) | Cited 5 times

Online Publication Date: 3 December 2002

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The oxidation of Co nanocolumns grown by the glancing angle deposition technique was studied ex situ using scanning tunneling microscopy and spectroscopy. The normalized conductance (dI/dV)/(I/V) of a single nanocolumn shows a nonoxidized Co peak at about −0.7 eV corresponding to the 3d valence electrons which was absent in the conventional film. It is argued that a retardation of the oxidation occurred in the Co nanocolumn due to the lack of grain boundaries in the isolated nanocolumns. © 2002 American Institute of Physics.
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81.65.Mq Oxidation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.16.Pr Micro- and nano-oxidation
61.46.-w Structure of nanoscale materials
FREE

Visible spectrum (654 nm) room temperature continuous wave InP quantum dot coupled to InGaP quantum well InP–InGaP–In(AlGa)P–InAlP heterostructure laser

G. Walter, N. Holonyak, R. D. Heller, and R. D. Dupuis

Appl. Phys. Lett. 81, 4604 (2002); http://dx.doi.org/10.1063/1.1526454 (3 pages) | Cited 10 times

Online Publication Date: 3 December 2002

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Data are presented demonstrating the cw 300 K visible spectrum (654 nm) laser operation of a single 7.5 monolayer InP quantum dot (QD) layer coupled by a 20 Å In0.5Al0.3Ga0.2P barrier to an auxiliary 70 Å In0.5Ga0.5P quantum well (QW) that, via resonant tunneling, assists carrier collection, thermalization, and lateral rearrangement in the QDs. The simple stripe-geometry (530 μm×10 μm) InP QD+InGaP QW heterostructure laser, enhanced by the QW and operating on an upper QD state (42% quantum efficiency), is capable of over 10 mW/facet cw 300 K operation in spite of the weak heat sinking of probe operation. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
73.21.La Quantum dots

Creation of a gradient polymer-fullerene interface in photovoltaic devices by thermally controlled interdiffusion

M. Drees, K. Premaratne, W. Graupner, J. R. Heflin, R. M. Davis, D. Marciu, and M. Miller

Appl. Phys. Lett. 81, 4607 (2002); http://dx.doi.org/10.1063/1.1522830 (3 pages) | Cited 32 times

Online Publication Date: 3 December 2002

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Efficient polymer-fullerene photovoltaic devices require close proximity of the two materials to ensure photoexcited electron transfer from the semiconducting polymer to the fullerene acceptor. We describe studies in which a bilayer system consisting of spin-cast 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene copolymer (MEH-PPV) and sublimed C60 is heated above the MEH-PPV glass transition temperature in an inert environment, inducing an interdiffusion of the polymer and the fullerene layers. With this process, a controlled, bulk, gradient heterojunction is created bringing the fullerene molecules within the exciton diffusion radius of the MEH-PPV throughout the film to achieve highly efficient charge separation. The interdiffused devices show a dramatic decrease in photoluminescence and concomitant increase in short circuit currents, demonstrating the improved interface. © 2002 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
85.60.-q Optoelectronic devices
81.05.ub Fullerenes and related materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
73.61.Wp Fullerenes and related materials
78.66.Tr Fullerenes and related materials
68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
61.46.-w Structure of nanoscale materials
66.30.Pa Diffusion in nanoscale solids
81.07.Bc Nanocrystalline materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.63.Bd Nanocrystalline materials
78.55.-m Photoluminescence, properties and materials
73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
81.16.-c Methods of micro- and nanofabrication and processing

Formation of oriented nanocrystals in an amorphous alloy by focused-ion-beam irradiation

R. Tarumi, K. Takashima, and Y. Higo

Appl. Phys. Lett. 81, 4610 (2002); http://dx.doi.org/10.1063/1.1526922 (3 pages) | Cited 24 times

Online Publication Date: 3 December 2002

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Structural changes of a Ni–P amorphous alloy under focused-ion-beam (FIB) irradiation have been examined using transmission electron microscopy. On the irradiated plane, the formation of crystallographically orientated nanosized crystals (NCs), with the particle size of approximately 10 nm, was observed. A series of electron diffraction analyses have revealed that NCs have a face-centered-cubic (fcc) structure and the following orientation relationships between the NCs and the FIB direction were found. These are, irradiated plane//(111)fcc and FIB direction//〈110〉fcc. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys

Fabrication of nanometer-spaced electrodes using gold nanoparticles

Saiful I. Khondaker and Zhen Yao

Appl. Phys. Lett. 81, 4613 (2002); http://dx.doi.org/10.1063/1.1528285 (3 pages) | Cited 46 times

Online Publication Date: 3 December 2002

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A simple and highly reproducible technique is demonstrated for the fabrication of metallic electrodes with nanometer separation. Commercially available bare gold colloidal nanoparticles are first trapped between prefabricated large-separation electrodes to form a low-resistance bridge by an ac electric field. A large dc voltage is then applied to break the bridge via electromigration at room temperature, which consistently produces gaps in the sub-10 nm range. The technique is readily applied to prefabricated electrodes with separation up to 1 μm, which can be defined using optical lithography. The simple fabrication scheme will facilitate electronic transport studies of individual nanostructures made by chemical synthesis. As an example, measurement of a thiol-coated gold nanoparticle showing a clear Coulomb staircase is presented. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
73.23.Hk Coulomb blockade; single-electron tunneling
61.46.-w Structure of nanoscale materials
82.70.Dd Colloids
66.30.Qa Electromigration

Laterally doped heterostructures for III–N lasing devices

S. M. Komirenko, K. W. Kim, V. A. Kochelap, and J. M. Zavada

Appl. Phys. Lett. 81, 4616 (2002); http://dx.doi.org/10.1063/1.1527985 (3 pages) | Cited 3 times

Online Publication Date: 3 December 2002

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To achieve a high-density electron-hole plasma in group-III nitrides for efficient light emission, we propose a planar two-dimensional (2D) p-i-n structure that can be formed in the quantum well layers due to efficient activation of donors and acceptors in the laterally, selectively doped barriers. We show that strongly nonequilibrium 2D electron-hole plasma with density above 1012 cm−2 can be realized in the i region of the laterally biased p-i-n structure, enabling the formation of interband population inversion and stimulated emission from such a lateral current pumped emitter (LACE). We suggest that implementation of the lateral p-i-n structures provides an efficient way of utilizing potential-profile-enhanced doping of superlattices and quantum wells for electric pumping of nitride-based lasers. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Pseudo-digital quantum bits

Mark Friesen, Robert Joynt, and M. A. Eriksson

Appl. Phys. Lett. 81, 4619 (2002); http://dx.doi.org/10.1063/1.1527692 (3 pages) | Cited 10 times

Online Publication Date: 3 December 2002

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Quantum computers are analog devices; thus they are highly susceptible to accumulative errors arising from classical control electronics. Fast operation—as necessitated by decoherence—makes gating errors very likely. In most current designs for scalable quantum computers, it is not possible to satisfy both the requirements of low decoherence errors and low gating errors. Here, we introduce a hardware-based technique for pseudo-digital gate operation. We perform self-consistent simulations of semiconductor quantum dots, finding that pseudo-digital techniques reduce operational error rates by more than two orders of magnitude, thus facilitating fast operation. © 2002 American Institute of Physics.
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03.67.Lx Quantum computation architectures and implementations

Thermal spike analysis of interface mixing induced by swift heavy ions

G. Szenes

Appl. Phys. Lett. 81, 4622 (2002); http://dx.doi.org/10.1063/1.1528303 (3 pages) | Cited 3 times

Online Publication Date: 3 December 2002

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Interface mixing induced by energetic ions is discussed, applying the author’s thermal spike model. Diffusion in the ion-induced melt is assumed. An expression is derived for the variation of the mixing rate k with the electronic stopping power Se. The experimental results recently reported by the Stuttgart group on NiO, ZnO, CuO, and Cu2O layers on SiO2 substrate are analyzed and good agreement is found with the predictions of the model for k and for the threshold of Se for melt formation. Average diffusion coefficients in the spike are estimated, and Dd ≈ 0.053, 0.03, and 0.004 cm2/s are obtained for Zn, Ni, and Cu ions, respectively. © 2002 American Institute of Physics.
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61.80.Jh Ion radiation effects
66.10.C- Diffusion and thermal diffusion
64.70.D- Solid-liquid transitions
61.82.Ms Insulators

Electrical resistivity of polypyrrole nanotube measured by conductive scanning probe microscope: The role of contact force

J. G. Park, S. H. Lee, B. Kim, and Y. W. Park

Appl. Phys. Lett. 81, 4625 (2002); http://dx.doi.org/10.1063/1.1528281 (3 pages) | Cited 40 times

Online Publication Date: 3 December 2002

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Polypyrrole (PPy) nanotubes were synthesized using the pores of track-etched polycarbonate membrane as a template. Its size depends on the pore diameter of template, range from 50 to 200 nm. Direct I–V measurements of PPy nanotube (diameter of 120 nm) deposited on Au were done using a metal-coated tapping-mode atomic-force-microscope tip. Linear I–V characteristics are observed, and the resistance is decreased as the contact force is increased. Using the Hertz model, the elastic modulus E and electrical resistivity ρ are estimated to be E ∼ 1 GPa and ρ ∼ 1 Ωcm. These values are consistent with those obtained in bulk PPy film. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
81.07.De Nanotubes
62.20.D- Elasticity
81.16.Ta Atom manipulation
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