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2 Apr 2001

Volume 78, Issue 14, pp. 1961-2084

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Epitaxial growth of Pb(Zr0.2Ti0.8)O3 on Si and its nanoscale piezoelectric properties

A. Lin, X. Hong, V. Wood, A. A. Verevkin, C. H. Ahn, R. A. McKee, F. J. Walker, and E. D. Specht

Appl. Phys. Lett. 78, 2034 (2001); http://dx.doi.org/10.1063/1.1358848 (3 pages) | Cited 29 times

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We have demonstrated a route to epitaxial Pb(Zr0.2Ti0.8)O3 on (001) Si that exhibits a uniform piezoelectric response down to nanoscale levels through the utilization of an insulating, single-crystalline SrTiO3 transition layer. These structures, which were grown by a combination of molecular-beam epitaxy and off-axis magnetron sputtering, have a surface roughness of <5 Å, with piezoelectric microscopy measurements revealing a piezoelectric coefficient of ∼50 pm/V that is switchable down to sub-100-nm dimensions. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Cd Deposition by sputtering

Origin and control of the lead-enriched near-surface region of (Pb, La)TiO3

E. Vasco, O. Böhme, E. Román, and C. Zaldo

Appl. Phys. Lett. 78, 2037 (2001); http://dx.doi.org/10.1063/1.1359484 (3 pages) | Cited 7 times

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The chemical composition, structure and extension of the Pb-enriched nonferroelectric near-surface region of stoichiometric (Pb, La)TiO3 ferroelectric films was characterized by x-ray diffraction, Rutherford backscattering spectroscopy and x-ray photoemission spectroscopy. Its origin as a result of the Pb excess segregation from the growing (Pb, La)TiO3 bulk and subsequent oxidation was revealed. A postdeposition procedure to control its composition and thereby its properties was provided. Thus, a decrease of the near-surface Pb excess of about 75% was achieved. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.35.Dv Composition, segregation; defects and impurities
77.55.-g Dielectric thin films
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Dp Adsorbed layers and thin films
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
81.15.Fg Pulsed laser ablation deposition
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Improvements in electrical properties of hydrogen-treated SrBi2Ta2O9 capacitors with chemical vapor deposited Pt top electrode

Eun-Suck Choi, Soon-Gil Yoon, and Won-Jae Lee

Appl. Phys. Lett. 78, 2040 (2001); http://dx.doi.org/10.1063/1.1347015 (3 pages)

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The ferroelectric property and leakage current of metalorganic chemical vapor deposition (MOCVD)-Pt/SrBi2Ta2O9 (SBT)/Pt and dc-sputtered Pt/SBT/Pt capacitors are evaluated with the microstructures of Pt top electrodes before and after hydrogen forming gas anneal. The SBT films with MOCVD-Pt top electrodes of large grain size and dense structure show a surprising decrease of leakage current density and still exhibit ferroelectric properties after hydrogen forming. On the other hand, SBT films with dc-sputtered Pt top electrodes of small grain size show an increase of leakage current density and then polarization switching properties cannot be measured due to fairly high leakage current. The microstructures of Pt top electrodes play an important role in improving the ferroelectric and leakage current characteristics after forming gas anneal. MOCVD-Pt top electrodes can prevent the complete loss of ferroelectricity and improve the leakage current properties during forming gas treatment. © 2001 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
81.65.Ps Polishing, grinding, surface finishing
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Monodispersed, nonagglomerated silicon nanocrystallites

Nobuyasu Suzuki, Toshiharu Makino, Yuka Yamada, Takehito Yoshida, and Takafumi Seto

Appl. Phys. Lett. 78, 2043 (2001); http://dx.doi.org/10.1063/1.1360236 (3 pages) | Cited 21 times

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We demonstrate the synthesis of monodispersed, nonagglomerated silicon (Si) nanocrystallites, using an integrated process system composed of a unit for the formation of nanocrystallites by pulsed-laser ablation in an inert background gas, a unit for classification using a differential mobility analyzer (DMA), and a unit for deposition onto a substrate using a nozzle jet. The DMA has been designed to operate under pressures less than 5.0 Torr. We have synthesized nonagglomerated Si nanocrystallites of 3.8 nm mean diameter and 1.2 geometrical standard deviation on carbon thin films using this integrated process system. © 2001 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.16.Mk Laser-assisted deposition
81.05.Cy Elemental semiconductors
61.46.-w Structure of nanoscale materials

Three-dimensional simulation of nanocrystal Flash memories

G. Iannaccone and P. Coli

Appl. Phys. Lett. 78, 2046 (2001); http://dx.doi.org/10.1063/1.1361097 (3 pages) | Cited 28 times

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We have developed a code for the detailed simulation of nanocrystal Flash memories, which consist of metal–oxide–semiconductor field-effect transistors (MOSFETs) with an array of semiconductor nanocrystals embedded in the gate dielectric. Information is encoded in the MOSFET threshold voltage, which depends on the amount of charge stored in the nanocrystal layer. Nanocrystals are charged through direct tunneling of electrons from the channel. Such memories are promising in terms of shorter write–erase times, larger cyclability, and lower power consumption with respect to conventional nonvolatile memories. We show results obtained from the self-consistent solution of the Poisson–Schrödinger equation on a three-dimensional grid, focusing on the charging process and on the effect of charge stored in the nanocrystals on the threshold voltage. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
81.16.-c Methods of micro- and nanofabrication and processing
84.30.Sk Pulse and digital circuits
73.63.-b Electronic transport in nanoscale materials and structures
85.30.De Semiconductor-device characterization, design, and modeling

Overlayer-induced anisotropic alignment of Nd2Fe14B nanograins

T. Shima, A. Kamegawa, K. Hono, and H. Fujimori

Appl. Phys. Lett. 78, 2049 (2001); http://dx.doi.org/10.1063/1.1360234 (3 pages) | Cited 11 times

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Highly anisotropic Nd2Fe14B thin film has been produced by triggering crystallization of sputter-deposited amorphous Nd–Fe–B layer by deposition of crystalline Cr overlayer. A downward growth of strongly textured Nd2Fe14B columnar grains was observed, starting from the interface between the Nd–Fe–B amorphous layer and the Cr overlayer. Cross-sectional transmission electron microscope observation results suggest that the possible mechanism of this peculiar crystallization is the heterogeneous nucleation at the surface of Nd–Fe–B amorphous layer, triggered by the crystalline Cr overlayer. © 2001 American Institute of Physics.
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75.50.Vv High coercivity materials
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
75.50.Bb Fe and its alloys

Template-based carbon nanotubes and their application to a field emitter

Soo-Hwan Jeong, Hee-Young Hwang, Kun-Hong Lee, and Yongsoo Jeong

Appl. Phys. Lett. 78, 2052 (2001); http://dx.doi.org/10.1063/1.1359483 (3 pages) | Cited 86 times

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Anodic aluminum oxide (AAO) templates were fabricated by anodizing Al films. After the Co catalyst had been electrochemically deposited into the bottom of the AAO template, carbon nanotubes (CNTs) were grown by the catalytic pyrolysis of C2H2 at 650 °C. Overgrowth of CNTs on the AAO templates was observed. The diameter of the CNTs strongly depends on the size of the pores in the AAO template. The electron field emission measurements on the samples showed a turn-on field of 1.9–2.1 V/μm and a field enhancement factor of 3360–5200. Our observation concerning the low turn-on field and high field enhancement factors is explained in terms of a low field screening effect. © 2001 American Institute of Physics.
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81.07.De Nanotubes
81.16.Be Chemical synthesis methods
79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Db Field emitters and arrays, cold electron emitters

Which nanowire couples better electrically to a metal contact: Armchair or zigzag nanotube?

M. P. Anantram

Appl. Phys. Lett. 78, 2055 (2001); http://dx.doi.org/10.1063/1.1360228 (3 pages) | Cited 18 times

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The fundamental question of how chirality affects the electronic coupling of a nanotube to metal contacts is important for the application of nanotubes as nanowires. We show that metallic-zigzag nanotubes are superior to armchair nanotubes as nanowires, by modeling the metal–nanotube interface. More specifically, we show that as a function of coupling strength, the total electron transmission of armchair nanotubes increases and tends to be pinned close to unity for a metal with Fermi wave vector close to that of gold. In contrast, the total transmission of zigzag nanotubes increases to the maximum possible value of two. The origin of these effects lies in the details of the wave function, which is explained. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
61.46.-w Structure of nanoscale materials
73.63.Fg Nanotubes
85.35.Kt Nanotube devices

Two field-emission states of single-walled carbon nanotubes

R. Collazo, R. Schlesser, and Z. Sitar

Appl. Phys. Lett. 78, 2058 (2001); http://dx.doi.org/10.1063/1.1361089 (3 pages) | Cited 21 times

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Two field-emission states of single-walled carbon nanotubes have been identified according to their respective emission current levels. The state yielding increased emission current has been attributed to the presence of adsorbates on the nanotubes. It was realized that, by application of high electric fields inducing large emission currents, a transition between the two states could be induced. For the high current state, field-emitted electrons originated from states located 1 eV below the Fermi level, as was determined by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface that enhanced the tunneling probability of the electrons. These states are removed when the nanotubes are cleaned by application of a large electric field, thus, decreasing the field-emitted current. © 2001 American Institute of Physics.
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71.20.Tx Fullerenes and related materials; intercalation compounds
79.70.+q Field emission, ionization, evaporation, and desorption
73.20.At Surface states, band structure, electron density of states

Mechanism of electron-beam writing in passivated gold nanoclusters

T. R. Bedson, R. E. Palmer, and J. P. Wilcoxon

Appl. Phys. Lett. 78, 2061 (2001); http://dx.doi.org/10.1063/1.1357210 (3 pages) | Cited 4 times

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We have investigated the mechanism of direct electron-beam writing in thin films of passivated gold nanoclusters. The exposure of films of approximately monolayer thickness (6 nm) was investigated as a function of electron dose on various substrates. Films were obtained on various substrates: graphite, silicon, thermally grown silicon dioxide and sputtered silicon dioxide. The experimental results are compared with Monte Carlo simulations of the electron scattering. We conclude that, in the case of such monolayer films, exposure of the clusters is dominated by electrons scattered in the substrate, so that the properties of the resist depend strongly on the nanocluster/substrate combination. © 2001 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
81.65.Rv Passivation
02.70.Uu Applications of Monte Carlo methods
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Electrical properties of three-terminal ballistic junctions

H. Q. Xu

Appl. Phys. Lett. 78, 2064 (2001); http://dx.doi.org/10.1063/1.1360229 (3 pages) | Cited 82 times

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Based on the ballistic nature of electron transport, exploitable nonlinear transport phenomena are predicted for three-terminal ballistic junctions (TBJs). For a symmetric TBJ, it is shown that when finite voltages Vl and Vr are applied in push-pull fashion, with Vl = V and Vr = −V, to the left and right branches, the voltage output Vc from the central branch will always be negative. This characteristic appears even when the device symmetry is broken, provided that ∣V∣ is greater than a certain threshold. It is also shown that the TBJs exhibit parabolic behavior for Vc vs V, in the weak nonlinear response regime. Potential applications of these devices in nanoelectronics are discussed. © 2001 American Institute of Physics.
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73.23.Ad Ballistic transport
73.63.Rt Nanoscale contacts
85.35.Ds Quantum interference devices

Integration of n-type and p-type quantum-well infrared photodetectors for sequential multicolor operation

E. Dupont, M. Gao, Z. Wasilewski, and H. C. Liu

Appl. Phys. Lett. 78, 2067 (2001); http://dx.doi.org/10.1063/1.1359482 (3 pages) | Cited 7 times

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A multicolor infrared photodetector based on the epitaxial integration of an n-type with a p-type GaAs/AlGaAs quantum-well stack is experimentally demonstrated. Additionally, a quantum-well GaAs light-emitting diode is inserted between the stacks to achieve up-conversion of mid-infrared radiation to near-infrared signal. This device shows a remarkable selectivity on wavelength: depending on the bias voltage the peak wavelength detection can be switched on and off between 9.1 and 4.85 μm. © 2001 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Pw Imaging detectors and sensors
78.67.De Quantum wells

Self-aligned double-gate single-electron transistor derived from 0.12-μm-scale electron-beam lithography

K. Nishiguchi and S. Oda

Appl. Phys. Lett. 78, 2070 (2001); http://dx.doi.org/10.1063/1.1360778 (3 pages) | Cited 9 times

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A single-electron transistor (SET) with two gates was fabricated via the self-aligned evaporation of Al into a trench structure comprised of Si and SiO2. The initial trench, which was comparable to 0.12 μm lines and defined by electron-beam lithography, was reduced to 0.05×0.02 μm by a slightly anisotropic etching characteristic. These processes allow for the production of SET devices using current silicon fabrication techniques. The simultaneous formation of two gates allows for one gate to be used to control the background charge of each device. The shift of Coulomb oscillation peaks was clearly shown by controlling the second gate bias. An inverter logic operation at a temperature of 5 K with a gain of 1.3 was obtained. These characteristics indicate that such SET logic devices, based on a combination of the good performance of the Al SET and the high level of control of the fabrication of Si technology, have considerable potential for future use. © 2001 American Institute of Physics.
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85.35.Gv Single electron devices
85.40.Hp Lithography, masks and pattern transfer
73.23.Hk Coulomb blockade; single-electron tunneling
84.30.Sk Pulse and digital circuits
81.65.Cf Surface cleaning, etching, patterning

Silicon carbide and silicon carbide:germanium heterostructure bipolar transistors

K. J. Roe, G. Katulka, J. Kolodzey, S. E. Saddow, and D. Jacobson

Appl. Phys. Lett. 78, 2073 (2001); http://dx.doi.org/10.1063/1.1358851 (3 pages) | Cited 15 times

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In this letter, we report on heterostructure bipolar transistors (HBTs) based on silicon carbide (SiC) and a silicon carbide:germanium (SiC:Ge) alloy. The SiC:Ge base alloy was formed by the ion implantation of Ge into p-type 4H–SiC and subsequent annealing. HBT mesa structures were fabricated using a reactive ion etching process. The incorporation of Ge was found to increase the gain and the Early voltage of the devices. A common-emitter current gain (β) of greater than 3 was measured for the SiC:Ge HBTs. Homojunction SiC transistors were fabricated as a reference using the same process (except no Ge in the base region) and exhibited a β of 2.2. The transistors exhibited high breakdown voltages (>50 V without passivation), that typify SiC-based devices. These results indicate that SiC:Ge is a promising material for use in SiC-based heterostructure devices. © 2001 American Institute of Physics.
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85.30.Pq Bipolar transistors
81.65.Cf Surface cleaning, etching, patterning
61.72.up Other materials
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing
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Near-field optical microscopy with a vibrating probe in aqueous solution

Anders Mannelquist, Hideki Iwamoto, Gabor Szabo, and Zhifeng Shao

Appl. Phys. Lett. 78, 2076 (2001); http://dx.doi.org/10.1063/1.1361088 (3 pages) | Cited 8 times

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We show that with an appropriately configured scanning quartz pipette coated with aluminum, a near-field scanning optical microscope (NSOM) can be constructed to operate in aqueous solution for applications in biology. Many of the technical limitations associated with a scanning pipette were circumvented by introducing a small modulation of the distance between the pipette and the sample. We show that this ac method allows the pipette to be positioned very close to the sample surface and is robust in obtaining reproducible NSOM images in solution. This approach is also compatible with fluorescence imaging and fluorescence resonance energy transfer, and should further facilitate the use of NSOM in various areas of cell biology where high resolution is considered to be critical. © 2001 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
87.64.mt Near-field scanning
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Resonance frequency shifts caused by the friction of a drop of water in air: An approach to estimate shear forces in scanning probe microscopies

A.-D. Müller and F. Müller

Appl. Phys. Lett. 78, 2079 (2001); http://dx.doi.org/10.1063/1.1361101 (3 pages) | Cited 1 time

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In scanning near-field optical microscopy, scanning ion conductance microscopy and for localized electrochemical deposition out of micropipettes, the detection of shear forces between the tip and sample is one of the most common methods of distance control. Here, pulled micropipettes were utilized to form an evaporating drop of water whose frictional force in air causes a specific resonance shift of the tip vibration. This resonance shift and the amplitude at the resonance were investigated with regard to their dependence on the drop diameter. In order to calculate the friction, the tip is approximated as a damped harmonic oscillator. The typical range of the shear forces in scanning probe microscopies is estimated to be between 1 pN and 0.1 nN. © 2001 American Institute of Physics.
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07.79.Sp Friction force microscopes
68.03.Fg Evaporation and condensation of liquids
68.37.Uv Near-field scanning microscopy and spectroscopy
64.70.F- Liquid-vapor transitions

Differential interference contrast x-ray microscopy with submicron resolution

Thomas Wilhein, Burkhard Kaulich, Enzo Di Fabrizio, Fillipo Romanato, Stefano Cabrini, and Jean Susini

Appl. Phys. Lett. 78, 2082 (2001); http://dx.doi.org/10.1063/1.1360776 (3 pages) | Cited 30 times

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Progress in lithography and nanofabrication [E. Di Fabrizio et al., Nature (London) 401, 895 (1999)] has made it possible to apply differential interference contrast (DIC) in x-ray microscopy using an original x-ray doublet lens based on two specially developed zone plates. Switching from bright-field imaging (absorption contrast) to x-ray DIC, we observe, similar to visible-light microscopy, a dramatic increase in image contrast for weak absorbing samples. We anticipate that this technique will have a significant impact on x-ray imaging and may play a role comparable to DIC imaging in visible-light microscopy. © 2001 American Institute of Physics.
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07.85.Tt X-ray microscopes
41.50.+h X-ray beams and x-ray optics
42.79.Ci Filters, zone plates, and polarizers
07.05.Pj Image processing
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