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10 Feb 2003

Volume 82, Issue 6, pp. 841-996

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 913 (2003); http://dx.doi.org/10.1063/1.1542686 (3 pages)

F. Gao and W. J. Weber
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Photocurrent method for characterizing the interface of hydrophobically bonded Si wafers

L. S. Yu, P. Mages, D. Qiao, L. Jia, P. K. L. Yu, S. S. Lau, T. Suni, K. Henttinen, and I. Suni

Appl. Phys. Lett. 82, 916 (2003); http://dx.doi.org/10.1063/1.1544063 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2003

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We report a simple and nondestructive photocurrent method for characterizing the bonding interface between two hydrophobically bonded Si wafers. The relationship of photocurrent versus wavelength was measured and analyzed. The direction of the photocurrent indicates the band-bending direction, and thus, the donor or acceptor nature of the interface states. The photocurrent is proportional to the electric field at the interface induced by band bending. Our results showed that the Si pairs bonded in air have much larger band bending at the interface than those bonded in dry nitrogen, and that both have donor-like interface states. © 2003 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
72.40.+w Photoconduction and photovoltaic effects
85.30.De Semiconductor-device characterization, design, and modeling
81.05.Cy Elemental semiconductors
72.80.Cw Elemental semiconductors
68.47.Fg Semiconductor surfaces

GaN growth using a low-temperature GaNP buffer on sapphire by metalorganic chemical vapor deposition

M. Tsukihara, Y. Naoi, S. Sakai, and H. D. Li

Appl. Phys. Lett. 82, 919 (2003); http://dx.doi.org/10.1063/1.1544061 (3 pages) | Cited 4 times

Online Publication Date: 4 February 2003

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We developed a buffer layer to grow GaN epilayers by metalorganic chemical vapor deposition. The buffer layer consists of a thin GaN-rich GaNP layer deposited at low temperature (LT) (500 °C) on sapphire substrate, using phosphine (PH3) as the phosphorus source. For high-temperature GaN epilayers grown on this type of buffer, full-width at half maximum values from both (0002) and (10math2) x-ray rocking curves decrease as phosphorus composition in the GaNP buffer increases; a dislocation density observed by transmission electron microscopy is as low as 5×108 cm−2, which is a factor of 2 less compared to that in a conventional GaN buffer epilayer. These results reveal that LT GaNP can be used as an appropriate buffer for further improving quality of GaN-based films. © 2003 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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HfO2-based insulating stacks on 4H–SiC(0001)

V. V. Afanas’ev, A. Stesmans, F. Chen, S. A. Campbell, and R. Smith

Appl. Phys. Lett. 82, 922 (2003); http://dx.doi.org/10.1063/1.1538310 (3 pages) | Cited 30 times

Online Publication Date: 4 February 2003

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Depositing HfO2 layers on ultrathin thermally grown SiO2 on 4H–SiC(0001) is demonstrated to yield an insulator with good properties. The stack combines the high quality of the ultrathin SiO2/SiC interface and associated high energy barriers for electron and hole injection from SiC with the high dielectric permittivity of HfO2 ( ≈ 20). The latter allows application of high electric fields to the SiC surface (up to 3 MV/cm), while keeping the strength of the field in the insulator at a moderate level. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Ch Permittivity (dielectric function)

Nonlinear hole transport through a submicron-size channel

O. Makarovsky, A. Neumann, A. M. Martin, L. Turyanska, A. Patanè, L. Eaves, M. Henini, P. C. Main, S. Thoms, C. D. W. Wilkinson, D. K. Maude, and J. C. Portal

Appl. Phys. Lett. 82, 925 (2003); http://dx.doi.org/10.1063/1.1543643 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2003

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We investigate hole transport through a submicron-size channel fabricated from a modulation-doped p-type GaAs/(AlGa)As single-quantum-well heterostructure. The intense electric field in the channel accelerates the holes beyond the inflection point of the lowest energy subband dispersion curve. This leads to current saturation and negative differential conduction effects in the current–voltage characteristics. © 2003 American Institute of Physics.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
73.50.Fq High-field and nonlinear effects
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Surface-induced phase separation in manganites: A microscopic origin for powder magnetoresistance

M. Bibes, Ll. Balcells, J. Fontcuberta, M. Wojcik, S. Nadolski, and E. Jedryka

Appl. Phys. Lett. 82, 928 (2003); http://dx.doi.org/10.1063/1.1543235 (3 pages) | Cited 32 times

Online Publication Date: 4 February 2003

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Through the analysis of the magnetic properties and of the nuclear magnetic resonance response of La2/3Ca1/3MnO3 ceramics with different grain sizes, we have found that poorly conducting regions, some ferromagnetic and some weakly magnetic, are located at the surface of the grains. We state that these regions constitute the tunnel barrier responsible for the low-field magnetoresistance usually observed in powders of half-metallic oxides. In addition, the spin disorder accompanying the coexistence of phases with different magnetoelectronic character could contribute to the large high-field magnetoresistance also typical of such ceramic samples. From a more general perspective, these findings can be of relevance to understand the microscopic origin of phase separation in manganites. © 2003 American Institute of Physics.
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75.47.Lx Magnetic oxides
75.70.Rf Surface magnetism
75.50.Tt Fine-particle systems; nanocrystalline materials
76.60.-k Nuclear magnetic resonance and relaxation
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Cc Other ferromagnetic metals and alloys

Noise sources and dissipation mechanisms of a 120 ℏ SQUID amplifier

Paolo Falferi, Michele Bonaldi, Antonella Cavalleri, Massimo Cerdonio, Andrea Vinante, Renato Mezzena, Ke-xi Xu, Giovanni Andrea Prodi, and Stefano Vitale

Appl. Phys. Lett. 82, 931 (2003); http://dx.doi.org/10.1063/1.1542673 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2003

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A two-stage superconducting quantum interference device (SQUID), based on a commercial sensor, is strongly coupled to an electrical resonator at 11 kHz with a quality factor Q = 600 000 and operated in the temperature range 1.33–4.17 K. From the analysis of the noise generated by this system, the back action noise of the SQUID amplifier is estimated. The minimum noise temperature, calculated from back action and additive noise measurements, is 63 μK at 1.33 K, and corresponds to 120 times the quantum-limited noise temperature. We discuss and experimentally verify a mechanism, which can limit the noise temperature and add losses to the system. © 2003 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.30.Le Amplifiers
07.50.Hp Electrical noise and shielding equipment

Enhancement of room-temperature magnetoresistance in Sr2FeMoO6 by reducing its grain size and adjusting its tunnel-barrier thickness

C. L. Yuan, Y. Zhu, and P. P. Ong

Appl. Phys. Lett. 82, 934 (2003); http://dx.doi.org/10.1063/1.1544066 (3 pages) | Cited 14 times

Online Publication Date: 4 February 2003

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The intergrain magnetoresistance (IMR) of polycrystalline Sr2FeMoO6 is known to depend on its grain size and the tunnel barrier thickness formed during fabrication. Further enhancement of the IMR of Sr2FeMoO6 is found possible by further decreasing its grain size using high-energy ball milling, as well as by judiciously adjusting the tunnel barrier thickness. The tunnel barrier thickness depends on the amount of insulating nonmagnetic SrMoO4 impurity formed during fabrication, which in turn can be controlled by varying the mixture ratio of the ambient gaseous H2–Ar stream during annealing. With smaller grain size, the magnetic domain size decreases correspondingly and so can be more easily rotated to produce a lower coercive field. The increase in the SrMoO4 impurity phase increases the number of grain boundary barriers in the Sr2FeMoO6 matrix, leading to a larger low-field magnetoresistance effect (LFMR). A significant enhancement of the LFMR was found when the SrMoO4 impurity was close to the conduction threshold. Compared to the artificial fabrication of multilayer structures, our method is much simpler and offers an enhanced technology to fabricate suitable tunneling barriers in magnetoresistive devices. © 2003 American Institute of Physics.
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75.47.Pq Other materials
61.72.Cc Kinetics of defect formation and annealing
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Induced magnetic anisotropy in amorphous ribbons by applying a magnetic field during the quenching process

M. Tejedor, J. A. García, J. Carrizo, L. Elbaile, and J. D. Santos

Appl. Phys. Lett. 82, 937 (2003); http://dx.doi.org/10.1063/1.1542675 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2003

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A method to induce magnetic anisotropy in amorphous magnetic ribbons has been developed. The anisotropy is induced in the high Curie temperature Fe80B20 and Co70Mn5Fe1Mo1Si14B9 amorphous magnetic ribbons by applying a magnetic field at the moment of the solidification of the melt. This method does not affect the excellent mechanical properties of these materials. The induced magnetic anisotropy has been measured by torque magnetometry and its strength and easy axis are compared with the results obtained by other authors using static magnetic annealing in similar samples. © 2003 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.30.Fb Solidification
81.40.Gh Other heat and thermomechanical treatments
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Open-type hybrid magnetic shield using high-TC superconducting wire and flexible magnetic sheets

Yusuke Seki, Daisuke Suzuki, Kuniomi Ogata, and Keiji Tsukada

Appl. Phys. Lett. 82, 940 (2003); http://dx.doi.org/10.1063/1.1544064 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2003

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An open-ended, cylindrical magnetic shield using high-TC superconducting rings and flexible magnetic sheets has been developed. The superconducting ring is made of Bi2Sr2Ca2Cu3Ox tape wire, and the flexible magnetic sheet is made of Fe–Cu–Nb–Si–B nanocrystalline alloy, which has superior soft magnetic properties. The superconducting rings are set near the open ends of a ferromagnetic cylinder. When a magnetic field is induced in the rings, a shielding current flows so as to keep the magnetic flux through the ring constant. It is concluded that the superconducting rings effectively increase the shielding factor of a magnetic shield. © 2003 American Institute of Physics.
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07.55.Nk Magnetic shielding in instruments
84.71.Mn Superconducting wires, fibers, and tapes

Pinning characteristics in chemically modified (Nd, Eu, Gd)–Ba–Cu–O superconductors

M. Muralidhar, N. Sakai, M. Nishiyama, M. Jirsa, T. Machi, and M. Murakami

Appl. Phys. Lett. 82, 943 (2003); http://dx.doi.org/10.1063/1.1542927 (3 pages) | Cited 22 times

Online Publication Date: 4 February 2003

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In melt-processed (Nd0.33Eu0.38Gd0.28)Ba2Cu3Oy (NEG-123) materials we found a new type of nanometer-scale pinning defects. Structural analysis was made with a dynamic force microscope and a scanning tunneling microscope (STM) that both showed the formation of a nanometer-scale lamellar structure. The high magnification STM showed that the nanolamellas are in fact rows (or planes) of aligned NEG-rich clusters 3–4 nm in size. This new pinning medium led to an increase of Birr at 77 K for the H∥ c axis up to 12 T (measured by a superconducting quantum interference device) or 15 T (measured by a vibrating sample magnetometer). A secondary peak as high as 70 kA/cm2 was observed at 4.5 T and decreased to 49 and 22 kA/cm2 at 7 and 10 T, respectively. © 2003 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
61.66.Bi Elemental solids
61.66.Dk Alloys
74.25.Ha Magnetic properties including vortex structures and related phenomena

FeCo–Zr–O nanogranular soft-magnetic thin films with a high magnetic flux density

S. Ohnuma, H. Fujimori, T. Masumoto, X. Y. Xiong, D. H. Ping, and K. Hono

Appl. Phys. Lett. 82, 946 (2003); http://dx.doi.org/10.1063/1.1537456 (3 pages) | Cited 24 times

Online Publication Date: 4 February 2003

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Soft-magnetic thin films with high magnetic flux densities of about 23 kG have been fabricated in the (Fe–Co)–Zr–O nanogranular system. The films were prepared by reactive sputtering under an oxygen–argon atmosphere using a target of Fe–Co–Zr alloys. The microstructure was composed of base-centered-cubic Fe–Co nanograins, where nanoparticles of amorphous Zr oxide are dispersed. These Zr-oxide nanoparticles are thought to hinder the growth of Fe–Co grains during the film deposition, causing low coercivity. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Dielectrophoretic assembly of oriented and switchable two-dimensional photonic crystals

Simon O. Lumsdon, Eric W. Kaler, Jacob P. Williams, and Orlin D. Velev

Appl. Phys. Lett. 82, 949 (2003); http://dx.doi.org/10.1063/1.1541114 (3 pages) | Cited 56 times

Online Publication Date: 4 February 2003

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We show that one- and two-dimensional crystals can be assembled from suspensions of latex or silica microspheres subjected to an alternating electric field in a gap between planar electrodes on a surface. These crystals, with areas above 25 mm2, are specifically oriented without the need for micropatterned templates. The order–disorder transitions take place within seconds and can be repeated tens of times by switching the field on and off. The particles accumulate on the surface between the electrodes due to the field gradient, align into rows along the field direction, and then crystallize into hexagonal arrays. The lattice spacings can be controlled via the electrostatic repulsion. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
68.35.Rh Phase transitions and critical phenomena
82.70.Dd Colloids
82.45.-h Electrochemistry and electrophoresis
42.82.Cr Fabrication techniques; lithography, pattern transfer

Complete suppression of filamentation and superior beam quality in quantum-dot lasers

Ch. Ribbat, R. L. Sellin, I. Kaiander, F. Hopfer, N. N. Ledentsov, D. Bimberg, A. R. Kovsh, V. M. Ustinov, A. E. Zhukov, and M. V. Maximov

Appl. Phys. Lett. 82, 952 (2003); http://dx.doi.org/10.1063/1.1533841 (3 pages) | Cited 45 times

Online Publication Date: 4 February 2003

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Comparative near-field and beam-quality (M2) measurements on narrow stripe quantum-dot (QD) and quantum-well (QW) lasers of identical structure, both emitting at 1100 nm, are presented. Intrinsic suppression of filamentation in the QD lasers is observed. QD lasers emitting at 1300 nm again show no filamentation. For a 6-μm-stripe, QW laser, M2 increases from 2.6 to 6.1 with output power increasing from 5 to 60 mW and with increasing stripe width (20 mW, 3→10 μm, M2 = 2.6→4.7). In the QD lasers, filamentation is suppressed up to 8 μm (1100 nm) and 9 μm (1300 nm) stripe width and no dependence on output power is observed. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Active planar optical waveguide made from luminescent silicon nanocrystals

J. Valenta, I. Pelant, K. Luterová, R. Tomasiunas, S. Cheylan, R. G. Elliman, J. Linnros, and B. Hönerlage

Appl. Phys. Lett. 82, 955 (2003); http://dx.doi.org/10.1063/1.1544433 (3 pages) | Cited 17 times

Online Publication Date: 4 February 2003

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We show experimentally that a layer of silicon nanocrystals, prepared by the Si-ion implantation (with the energy of 400 keV) into a synthetic silica slab and exhibiting room-temperature red photoluminescence, can serve simultaneously as a single-mode planar optical waveguide. The waveguide is shown to self-select guided transverse electric and transverse magnetic modes from the broad photoluminescence emission of the nanocrystals resulting in a substantially narrower emission spectrum for these modes. We further report on an investigation of optical gain in a sample implanted to a dose of 4×1017 cm−2. Despite the occurrence of strong waveguiding, results of the variable stripe length method turned out not to be able to give unambiguous evidence for optical gain. © 2003 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.uf Ge and Si

Ultrafast optical Kerr effect of Ag–BaO composite thin films

Q. F. Zhang, W. M. Liu, Z. Q. Xue, J. L. Wu, S. F. Wang, D. L. Wang, and Q. H. Gong

Appl. Phys. Lett. 82, 958 (2003); http://dx.doi.org/10.1063/1.1541092 (3 pages) | Cited 30 times

Online Publication Date: 4 February 2003

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We report the ultrafast optical Kerr effect of Ag–BaO composite thin films by the femtosecond time-resolved pump-probe technique. The Ag–BaO thin films with Ag nanoparticles embedded into the BaO semiconductor matrix were prepared using a vacuum evaporation-deposition multimetallic layer method. The third-order nonlinear optical susceptibility of the thin films with the thickness of approximately 300 nm and the volume fraction of Ag nanoparticles in the thin films of about 25% was estimated to be 4.8×10−10 esu at the incident laser wavelength of 820 nm. The response time, i.e., the full width at half maximum of the Kerr signal, was as fast as 210 fs. The intrinsic third-order optical nonlinearity, or the optical Kerr effect of the thin films, can be attributed to the change of refractive index due to the intraband transition of electrons from the occupied state near the Fermi level to the unoccupied state in the Ag nanoparticles. Such nonlinearity is further enhanced by the local field effect that is present when the metallic nanoparticles are embedded into the semiconductor matrix. © 2003 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.An Optical susceptibility, hyperpolarizability
81.07.Bc Nanocrystalline materials
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Sensors for sub-ppm NO2 gas detection based on carbon nanotube thin films

L. Valentini, I. Armentano, J. M. Kenny, C. Cantalini, L. Lozzi, and S. Santucci

Appl. Phys. Lett. 82, 961 (2003); http://dx.doi.org/10.1063/1.1545166 (3 pages) | Cited 150 times

Online Publication Date: 4 February 2003

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Carbon nanotubes (CNTs) deposited by plasma-enhanced chemical vapor deposition on Si3N4/Si substrates have been investigated as resistive gas sensors for NO2. Upon exposure to NO2, the electrical resistance of the CNTs was found to decrease. The maximum variation of resistance to NO2 was found at an operating temperature of around 165 °C. The sensor exhibited high sensitivity to NO2 gas at concentrations as low as 10 ppb, fast response time, and good selectivity. A thermal treatment method, based on repeated heating and cooling of the films, adjusted the resistance of the sensor film and optimized the sensor response to NO2. © 2003 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.35.Kt Nanotube devices
82.80.-d Chemical analysis and related physical methods of analysis

Excitonic emissions observed in ZnO single crystal nanorods

W. I. Park, Y. H. Jun, S. W. Jung, and Gyu-Chul Yi

Appl. Phys. Lett. 82, 964 (2003); http://dx.doi.org/10.1063/1.1544437 (3 pages) | Cited 176 times

Online Publication Date: 4 February 2003

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We report on the photoluminescent characteristics of ZnO single crystal nanorods grown by catalyst-free metalorganic vapor phase epitaxy. From photoluminescence (PL) spectra of the nanorods at 10 K, several PL peaks were observed at 3.376, 3.364, 3.360, and 3.359 eV. The PL peak at 3.376 eV is attributed to a free exciton peak while the other peaks are ascribed to neutral donor bound exciton peaks. The observation of the free exciton peak at 10 K indicates that ZnO nanorods prepared by the catalyst-free method are of high optical quality. © 2003 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.21.Hb Quantum wires
73.22.Lp Collective excitations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Bc Nanocrystalline materials

Highly-ordered GaAs/AlGaAs quantum-dot arrays on GaAs (001) substrates grown by molecular-beam epitaxy using nanochannel alumina masks

X. Mei, M. Blumin, M. Sun, D. Kim, Z. H. Wu, H. E. Ruda, and Q. X. Guo

Appl. Phys. Lett. 82, 967 (2003); http://dx.doi.org/10.1063/1.1544065 (3 pages) | Cited 22 times

Online Publication Date: 4 February 2003

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Highly-ordered GaAs/AlGaAs quantum-dot arrays (QDA) were grown by molecular-beam epitaxy on GaAs (001) using masks of anodic nanochannel alumina (NCA). The QDA replicated the hexagonal lattice pattern of the NCA masks with period spacing of 100 nm. The circular disk-like dots were defined by the nanohole channels of NCA masks with size adjustable between 45 and 85 nm. Both single- and double-well GaAs/AlGaAs QDA exhibited strong photoluminescence. The single-well QDA showed a narrow peak at 1.64 eV with full width at half maximum of only 16 meV, indicating good size uniformity and crystal quality for the QDA. NCA masked epitaxial growth is thus shown to be a promising general approach for fabricating various heterostructure QDA, including both strained and lattice-matched heterostructures. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Temperature dependence of superconductor-correlated metal–superconductor Josephson junctions

J. K. Freericks, B. K. Nikolić, and P. Miller

Appl. Phys. Lett. 82, 970 (2003); http://dx.doi.org/10.1063/1.1543236 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2003

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Josephson junctions, with the barrier composed of a correlated metal (or insulator) tuned to lie close to the metal–insulator transition, show promise to provide the fastest operating speeds for digital electronics based on rapid single-flux quantum logic. We provide theoretical calculations that indicate that these devices have a small enough temperature derivative of Ic(T) within the junction operating range to allow them to be employed as elements in complex digital circuits. © 2003 American Institute of Physics.
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85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
85.25.Cp Josephson devices
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.25.Sv Critical currents

Formation of nanofiber crossbars in electrospinning

E. Zussman, A. Theron, and A. L. Yarin

Appl. Phys. Lett. 82, 973 (2003); http://dx.doi.org/10.1063/1.1544060 (3 pages) | Cited 105 times

Online Publication Date: 4 February 2003

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In this letter, we report on a technique for the hierarchical assembly of nanofibers into crossbar nanostructures. An electrospinning process is used to create polymer-based nanofibers with diameters ranging from 10–180 nm and lengths of up to several centimeters. By controlling the electrostatic field and the polymer rheology, the nanofibers can be assembled into parallel periodic arrays. We also propose a theoretical model for the process. © 2003 American Institute of Physics.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
47.65.-d Magnetohydrodynamics and electrohydrodynamics
83.80.Rs Polymer solutions
61.46.-w Structure of nanoscale materials
61.41.+e Polymers, elastomers, and plastics

Vertically aligned carbon nanofibers as sacrificial templates for nanofluidic structures

A. V. Melechko, T. E. McKnight, M. A. Guillorn, V. I. Merkulov, B. Ilic, M. J. Doktycz, D. H. Lowndes, and M. L. Simpson

Appl. Phys. Lett. 82, 976 (2003); http://dx.doi.org/10.1063/1.1544058 (3 pages) | Cited 13 times

Online Publication Date: 4 February 2003

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We report a method to fabricate nanoscale pipes (“nanopipes”) suitable for fluidic transport. Vertically aligned carbon nanofibers grown by plasma-enhanced chemical vapor deposition are used as sacrificial templates for nanopipes with internal diameters as small as 30 nm and lengths up to several micrometers that are oriented perpendicular to the substrate. This method provides a high level of control over the nanopipe location, number, length, and diameter, permitting them to be deterministically positioned on a substrate and arranged into arrays. © 2003 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
81.07.Bc Nanocrystalline materials
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.Dn Self-assembly
61.46.-w Structure of nanoscale materials
47.85.Np Fluidics
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Formation mechanism of nanocatalysts for the growth of silicon nanowires on a hydrogen-terminated Si {111} surface template

S. Takeda, K. Ueda, N. Ozaki, and Y. Ohno

Appl. Phys. Lett. 82, 979 (2003); http://dx.doi.org/10.1063/1.1541934 (3 pages) | Cited 10 times

Online Publication Date: 4 February 2003

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We have observed the formation process of nanocatalysts that act for the growth of Si nanowires by means of UHV scanning tunneling microscopy. Gold–silicon nanocatalysts that we have examined were thought to form on a hydrogen (H)-terminated [111] silicon surface and to expel Si nanowires of extremely high aspect ratio via the vapor-liquid-solid mechanism. We have observed that a nanocatalyst, that is, a droplet of melted gold–silicon alloy of about 5 nm in diameter, is actually formed in a pit on a H-terminated surface in the narrow temperature range around 500 °C. We have concluded that, in this specific temperature range, nanocatalysts can be melted, remain mutually isolated, absorb silicon effectively, and expel Si nanowires. Based on the result, we have proposed a method of making a thin template, which facilitates to decide the nucleation sites and the sizes of nanocatalysts, resulting in the precise control of those of Si nanowires. © 2003 American Institute of Physics.
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81.16.Hc Catalytic methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
68.47.Fg Semiconductor surfaces
81.05.Cy Elemental semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
64.70.D- Solid-liquid transitions
82.60.Nh Thermodynamics of nucleation

Characterization of the nanostructures of a lithographically patterned dot array by x-ray pseudo-Kossel lines

D. R. Lee, Y. S. Chu, Y. Choi, J. C. Lang, G. Srajer, S. K. Sinha, V. Metlushko, and B. Ilic

Appl. Phys. Lett. 82, 982 (2003); http://dx.doi.org/10.1063/1.1543249 (3 pages) | Cited 8 times

Online Publication Date: 4 February 2003

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Grazing x-ray scattering from a nanofabricated periodic dot array exhibits an interesting diffraction pattern, resembling x-ray Kossel lines, due to the anisotropic x-ray resolution function. We demonstrate that the unique diffraction pattern can be used for precise characterization of the deep nanostructures, which cannot be obtained accurately by microscopy techniques. © 2003 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cp X-ray diffraction
61.46.-w Structure of nanoscale materials
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Electro-optical properties of a polymer light-emitting diode with an injection-limited hole contact

T. van Woudenbergh, P. W. M. Blom, and J. N. Huiberts

Appl. Phys. Lett. 82, 985 (2003); http://dx.doi.org/10.1063/1.1543255 (3 pages) | Cited 25 times

Online Publication Date: 4 February 2003

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The electro-optical characteristics of a polymer light-emitting diode with a strongly reduced hole injection have been investigated. A silver contact on poly-dialkoxy-p-phenylene vinylene decreases the hole injection by five orders of magnitude, resulting in both a highly reduced light output and current. However, at high applied voltages, the current and light output strongly exceed the predictions based on the reduced hole injection, which is explained by an enhanced electric field near the hole-injection contact due to trapped electrons. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.40.Ns Metal-nonmetal contacts
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds

Fabrication of in-plane gate transistors on hydrogenated diamond surfaces

J. A. Garrido, C. E. Nebel, R. Todt, G. Rösel, M.-C. Amann, M. Stutzmann, E. Snidero, and P. Bergonzo

Appl. Phys. Lett. 82, 988 (2003); http://dx.doi.org/10.1063/1.1545152 (3 pages) | Cited 23 times

Online Publication Date: 4 February 2003

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The highly conductive surface layer induced in diamond by hydrogen termination has been used to fabricate in-plane gate transistors. The conductive channel has been separated from the Ohmic gate contacts by insulating thin lines, obtained by using a combination of electron-beam lithography with surface oxidation. Oxidized lines of about 100 nm show excellent blocking properties, with leakage current of 0.3 pA/μm at 100 V and room temperature. In-plane transistor properties are reported for operation at 77 K and room temperature with good saturation characteristic and complete pinch-off. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Mq Oxidation
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