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16 Sep 2002

Volume 81, Issue 12, pp. 2145-2305

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Structural studies of L10 FePt nanoparticles

T. J. Klemmer, N. Shukla, C. Liu, X. W. Wu, E. B. Svedberg, O. Mryasov, R. W. Chantrell, D. Weller, M. Tanase, and D. E. Laughlin

Appl. Phys. Lett. 81, 2220 (2002); http://dx.doi.org/10.1063/1.1507837 (3 pages) | Cited 53 times

Online Publication Date: 9 September 2002

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We have studied the lattice parameter changes of L10 FePt nanoparticles annealed to near equilibrium as a function of composition by x-ray diffraction. We have found that the (111) diffraction peak shifts linearly with composition, however, the c parameter mostly changes in the Pt rich compositions and the a parameter mostly changes in the Fe rich compositions with respect to the equiatomic composition. This causes the tetragonality of the L10 structure to be maximized near the Fe 50%/Pt 50% composition. The magnetic properties were measured at room temperature and at 5 K and are correlated to the structural changes occurring as a function of composition. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
61.66.Dk Alloys
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Vibrational mode analysis of β-phase poly(vinylidene fluoride)

J. C. Li, C. L. Wang, W. L. Zhong, P. L. Zhang, Q. H. Wang, and J. F. Webb

Appl. Phys. Lett. 81, 2223 (2002); http://dx.doi.org/10.1063/1.1507356 (3 pages) | Cited 17 times

Online Publication Date: 9 September 2002

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The infrared spectrum of β-phase poly(vinylidene fluoride) (PVDF) film (30 μm) in the region from 4000 to 400 cm−1 has been measured. The vibrational frequencies of all-trans chains of PVDF have been calculated from first principles based on a restricted Hartree–Fock self-consistent field method. The calculated result is in good agreement with the experiment. All the vibrational modes were divided into three types, only one of them which is in the region from 1330 to 1020 cm−1, corresponds to a changing dipole moment, and may be responsible for the spontaneous polarization. © 2002 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
78.30.Jw Organic compounds, polymers
63.20.-e Phonons in crystal lattices
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
78.66.Qn Polymers; organic compounds

Dielectric and ferroelectric anisotropy of intergrowth Bi4Ti3O12–PbBi4Ti4O15 single crystals

Yu Goshima, Yuji Noguchi, and Masaru Miyayama

Appl. Phys. Lett. 81, 2226 (2002); http://dx.doi.org/10.1063/1.1506791 (3 pages) | Cited 22 times

Online Publication Date: 9 September 2002

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Intergrowth Bi4Ti3O12–PbBi4Ti4O15 single crystals were grown, and their dielectric and ferroelectric anisotropy were investigated along the a and c axes. Dielectric measurements revealed that the Curie temperature was 550 °C, which was lower than that of Bi4Ti3O12 (675 °C) and PbBi4Ti4O15 (570 °C). Remanent polarization was observed for intergrowth oxides not only along the a axis but also along the c axis, and the c-axis component is suggested to originate from Bi4Ti3O12 layers in the intergrowth structure. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis

Approach for enhanced polarization of polycrystalline bismuth titanate films by Nd3+/V5+ cosubstitution

Hiroshi Uchida, Hiroki Yoshikawa, Isao Okada, Hirofumi Matsuda, Takashi Iijima, Takayuki Watanabe, Takashi Kojima, and Hiroshi Funakubo

Appl. Phys. Lett. 81, 2229 (2002); http://dx.doi.org/10.1063/1.1507839 (3 pages) | Cited 73 times

Online Publication Date: 9 September 2002

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Thin films of Nd3+-substituted bismuth titanate, (Bi4.00−y,Ndy)Ti3.00O12 (BNT), Nd3+/V5+-cosubstituted bismuth titanate, (Bi4.00−y,Ndy)(Ti3.00−xVx)O12 (BNTV), and La3+-substituted bismuth titanate, (Bi3.25,La0.75)Ti3.00O12 (BLT) were fabricated on the (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution deposition technique. These films possessed random-oriented polycrystalline structure. The BNT film had larger remnant polarization (Pr) than the BLT film; Pr and coercive field (Ec) of the BNT film with y = 0.50 were 32 μC/cm2 and 126 kV/cm, respectively. Furthermore, V5+ substitution improved the Pr value of the BNT film up to 37 μC/cm2 (BNTV film; y = 0.50, x = 0.02), while the BNTV film had an Ec value of approximately 119 kV/cm which was similar to that of the BNT film. Ferroelectric properties of the Pb-free polycrystalline BNT and BNTV films are comparable with those of conventional Pb-based ferroelectric films like a lead zirconate titanate. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity

Pore size distributions in nanoporous methyl silsesquioxane films as determined by small angle x-ray scattering

E. Huang, M. F. Toney, W. Volksen, D. Mecerreyes, P. Brock, H.-C. Kim, C. J. Hawker, J. L. Hedrick, V. Y. Lee, T. Magbitang, R. D. Miller, and L. B. Lurio

Appl. Phys. Lett. 81, 2232 (2002); http://dx.doi.org/10.1063/1.1507841 (3 pages) | Cited 34 times

Online Publication Date: 9 September 2002

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Small angle x-ray scattering (SAXS) measurements were performed on nanoporous methyl silsesquioxane films that were generated by the incorporation of a sacrificial polymeric component into the matrix and subsequently removed by thermolysis. The average pore radii ranged from 1 to 5 nm over a porosity range of ∼ 5–50%. The distribution in pore size was relatively broad and increases in breadth with porosity. The values and observations obtained by SAXS are in good agreement with field emission scanning electron microscopy. © 2002 American Institute of Physics.
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61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
78.70.Ck X-ray scattering
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Morphology and electronic structure in nitrogen-doped ultrananocrystalline diamond

James Birrell, J. A. Carlisle, O. Auciello, D. M. Gruen, and J. M. Gibson

Appl. Phys. Lett. 81, 2235 (2002); http://dx.doi.org/10.1063/1.1503153 (3 pages) | Cited 75 times

Online Publication Date: 9 September 2002

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Ultrananocrystalline diamond (UNCD) thin films consist of 2–5 nm grains of pure sp3-bonded carbon and ∼0.5-nm-wide grain boundaries with a disordered mixture of sp2- and sp3-bonded carbon. UNCD exhibits many interesting materials properties that are a direct consequence of its nanoscale morphology. In this work, we report the changes in morphology induced in UNCD by the addition of nitrogen gas to the Ar/CH4 microwave plasma, as studied using high-resolution transmission electron microscopy and nanoprobe-based electron energy-loss spectroscopy. Both the grain size and grain-boundary widths increase with the addition of N2, but the overall bonding structure in both regions remains mostly unchanged. These results are used to explain the variation of materials properties of nitrogen-incorporated UNCD films. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
68.55.-a Thin film structure and morphology
61.72.Mm Grain and twin boundaries
81.05.U- Carbon/carbon-based materials
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Bc Nanocrystalline materials

Laser-induced lateral epitaxy in fully depleted silicon-on-insulator junctions

Kevin K. Dezfulian, J. Peter Krusius, Michael O. Thompson, and Somit Talwar

Appl. Phys. Lett. 81, 2238 (2002); http://dx.doi.org/10.1063/1.1507359 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2002

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Junction formation by laser-induced lateral epitaxy was studied on a fully depleted silicon-on-insulator substrate (25–30 nm Si on 375 nm silicon dioxide). Selective laser melting of amorphous films with a 35 ns 308 nm XeCl laser pulse was characterized in situ using transient conduction and optical reflectance techniques. Lateral epitaxy from a channel edge was observed for 146 nm after a 300 mJ/cm2 irradiation. The initial 28 nm of epitaxy was nearly defect free, followed by an increasing density of twins and ultimately terminating in an amorphous quench. The microstructure is discussed as a lateral equivalent of laser-induced amorphization of bulk Si. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Mechanism for grain size softening in nanocrystalline Zn

Hans Conrad and J. Narayan

Appl. Phys. Lett. 81, 2241 (2002); http://dx.doi.org/10.1063/1.1507353 (3 pages) | Cited 23 times

Online Publication Date: 9 September 2002

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A technique (laser deposition of Zn/W multilayers) for producing stable nanocrystalline (nc) Zn films free of undesirable imperfections down to a grain size of d = 6 nm is presented. These films exhibited grain size softening (inverse Hall–Petch effect) for d ⩽ 11 nm, providing support that this can be a real phenomenon in nc solids. The mechanism responsible for the softening was concluded to be thermally activated grain boundary shear. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
81.07.Bc Nanocrystalline materials
61.72.Mm Grain and twin boundaries
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.15.Fg Pulsed laser ablation deposition

Kinetics of boron reactivation in doped silicon from Hall effect and spreading resistance techniques

Aaron D. Lilak, Mark E. Law, Ljubo Radic, Kevin S. Jones, and Mark Clark

Appl. Phys. Lett. 81, 2244 (2002); http://dx.doi.org/10.1063/1.1508438 (3 pages) | Cited 15 times

Online Publication Date: 9 September 2002

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In this work, a series of 13 boron implants were performed into Czochralski silicon substrates with doses of 2×1014–1.6×1015 cm−2 at energies of 10–80 keV. The boron was deliberately clustered with a 750 °C anneal of 10 or 30 min and the electrical activation of the boron implants was determined following a second anneal at 750 or 850 °C with a Hall effect system with certain samples also being analyzed with a spreading resistance technique. Analysis of the reactivation rates allows for the determination of the net energy to boron reactivation to be approximately 3.0 eV assuming the reactivation process is mediated by release of a boron interstitial with a migrational energy of 0.3 eV. This results in a critical binding energy of approximately 2.7 eV from the process limiting the dissolution of the most stable boron-interstitial cluster. © 2002 American Institute of Physics.
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61.72.uf Ge and Si
71.55.Cn Elemental semiconductors
81.05.Cy Elemental semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
72.80.Cw Elemental semiconductors

Switching times in electric-field-tunable GaAs/AlAs heterostructures

F. J. Ribeiro, R. B. Capaz, and Belita Koiller

Appl. Phys. Lett. 81, 2247 (2002); http://dx.doi.org/10.1063/1.1507621 (3 pages) | Cited 2 times

Online Publication Date: 9 September 2002

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Optical experiments on electric-field-tunable AlAs/GaAs heterostructures demonstrate that the optical nature of these structures can be directly controlled by an applied electric field. We present calculations performed within the tight-binding supercell formalism, taking into account the effects of the heterostructure geometry and of the external uniform electric field. We describe the temporal and spatial evolution of the relevant electronic states. The electric-field intensity needed to cause the indirect–direct transition is obtained in good agreement with the experimental results for comparable heterostructure geometry. We present simple and reliable expressions to estimate the switching time scales involved in such processes. © 2002 American Institute of Physics.
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78.67.De Quantum wells
78.20.Jq Electro-optical effects
73.21.Fg Quantum wells
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Charge transfer control by gate voltage in crossed nanotube junction

Nobuhide Yoneya, Kazuhito Tsukagoshi, and Yoshinobu Aoyagi

Appl. Phys. Lett. 81, 2250 (2002); http://dx.doi.org/10.1063/1.1508160 (3 pages) | Cited 6 times

Online Publication Date: 9 September 2002

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We report the control of charge transfer between two crossed multiwalled carbon nanotubes (MWNTs) in a flash-memory-device configuration. An upper MWNT was used as the current channel and a second MWNT was used as the floating node underneath the channel MWNT. In this device, the source-drain current showed a clear hysteresis loop in a cyclic scan of gate voltage below 40 K. This hysteresis loop was caused by charging and discharging in the floating MWNT, and the resistance of the channel MWNT was switched between high and low. This hysteresis loop indicates that the controllable charges transferred between the two crossed MWNTs are detectable during a resistance change due to the Coulomb potential. © 2002 American Institute of Physics.
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85.35.Kt Nanotube devices
84.30.Sk Pulse and digital circuits
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Tv Field effect devices

Balanced electronic detection of displacement in nanoelectromechanical systems

K. L. Ekinci, Y. T. Yang, X. M. H. Huang, and M. L. Roukes

Appl. Phys. Lett. 81, 2253 (2002); http://dx.doi.org/10.1063/1.1507833 (3 pages) | Cited 39 times

Online Publication Date: 9 September 2002

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We describe a broadband radio frequency balanced bridge technique for electronic detection of displacement in nanoelectromechanical systems (NEMS). With its two-port actuation-detection configuration, this approach generates a background-nulled electromotive force in a dc magnetic field that is proportional to the displacement of the NEMS resonator. We demonstrate the effectiveness of the technique by detecting small impedance changes originating from NEMS electromechanical resonances that are accompanied by large static background impedances at very high frequencies. This technique allows the study of important experimental systems such as doped semiconductor NEMS and may provide benefits to other high frequency displacement transduction circuits. © 2002 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment

Direct observation of magnetization switching in focused-ion-beam-fabricated magnetic nanotubes

Sakhrat Khizroev, Mark H. Kryder, Dmitri Litvinov, and David A. Thompson

Appl. Phys. Lett. 81, 2256 (2002); http://dx.doi.org/10.1063/1.1508164 (2 pages) | Cited 25 times

Online Publication Date: 9 September 2002

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In this letter, a direct measurement of “easy” magnetization switching indicating zero-magnetization remanence in a magnetic probe with a cross section as narrow as 60×60 nm2, and as tall as 750 nm, is presented. Magnetic force microscopy was utilized to test focused-ion-beam-fabricated nanomagnetic probes. The data directly indicate that unlike a regular solid probe, a probe with a tubelike ending (nanotube) provides substantially “easier” switching. © 2002 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
81.07.De Nanotubes
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
81.65.Cf Surface cleaning, etching, patterning

Piezoelectric displacement sensing with a single-electron transistor

R. Knobel and A. N. Cleland

Appl. Phys. Lett. 81, 2258 (2002); http://dx.doi.org/10.1063/1.1507616 (3 pages) | Cited 21 times

Online Publication Date: 9 September 2002

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We propose a displacement sensing scheme for rf mechanical resonators made from GaAs, based on detecting the piezoelectrically induced charge. By using a single-electron transistor to detect the charge, we calculate that a significantly higher displacement sensitivity can be achieved than by using capacitive displacement sensing, primarily due to the strong piezoelectric coupling strength. We estimate a displacement sensitivity of order 10−17 m/Hz1/2 for a 1 GHz GaAs resonator. Our model solves the coupled electromechanical response self-consistently, including the effects of both dissipative and reactive electronic circuit elements on the resonator behavior. © 2002 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.65.Fs Electromechanical resonance; quartz resonators

Growth of suspended carbon nanotube networks on 100-nm-scale silicon pillars

Yoshikazu Homma, Yoshihiro Kobayashi, Toshio Ogino, and Takayuki Yamashita

Appl. Phys. Lett. 81, 2261 (2002); http://dx.doi.org/10.1063/1.1507840 (3 pages) | Cited 60 times

Online Publication Date: 9 September 2002

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We investigated carbon nanotube growth by means of methane chemical vapor deposition on ultrafine silicon patterns prepared by synchrotron-radiation lithography. Grown nanotubes formed suspended bridges between pillars when pillar spacing was comparable to pillar height. Network-like interconnections were obtained on pillar arrays. Nearest-neighbor bridging accounted for more than 80% of all the bridging nanotubes. The self-directed growth between neighboring pillars may be explained by the swing of the nanotube cantilever which contacts a catalyst particle in liquid phase as the nanotube grows. These results confirm the possibility of self-assembled wiring of nanostructures. © 2002 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
61.46.-w Structure of nanoscale materials
85.40.Hp Lithography, masks and pattern transfer

Electron transport through quantum-dot states of n-type carbon nanotubes

Yong-Hyun Kim and K. J. Chang

Appl. Phys. Lett. 81, 2264 (2002); http://dx.doi.org/10.1063/1.1508415 (3 pages) | Cited 1 time

Online Publication Date: 9 September 2002

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We calculate electron transmission in carbon nanotube field-effect-transistors, based on a tight-binding model. For positive gate voltages, a quantum dot is formed in the nanotube between two regions doped p type by metal contacts, and the resulting quantum dot states give rise to n-type conduction. While p-type currents for negative gate voltages exhibit robustness, n currents sensitively depend on the depletion layer between regions doped p type by the contacts and n type by the gate. This feature explains the polarity of electron transport observed in carbon nanotube transistors. © 2002 American Institute of Physics.
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85.35.Kt Nanotube devices
73.63.Fg Nanotubes
73.21.La Quantum dots
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Synthesis, Raman scattering and defects of β-Ga2O3 nanorods

Y. H. Gao, Y. Bando, T. Sato, Y. F. Zhang, and X. Q. Gao

Appl. Phys. Lett. 81, 2267 (2002); http://dx.doi.org/10.1063/1.1507835 (3 pages) | Cited 35 times

Online Publication Date: 9 September 2002

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Large yield of β-Ga2O3 nanorods with metal Ga tip were efficiently synthesized. They were deposited on surface of amorphous C fibers by decomposition of Ga2O vapor at around 1000 °C, where Ga2O vapor was produced at 1360 °C by a reaction between pure Ga2O3 and active carbon powders. The nanorods had diameters ranging from 10 to 100 nm and lengths of up to several tens micrometers. Twins and edge dislocations having a Burgers vector of 0.0859 Å [2.66, 3.66, math] existed in the nanorods. A redshift of 4–23 cm−1 was found in the Raman scattering spectrum of nanorods compared with that of a pure Ga2O3 powder. This phenomenon was explained qualitatively in terms of the defects in the nanorods. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.16.Be Chemical synthesis methods
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials
61.72.Mm Grain and twin boundaries
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.30.Hv Other nonmetallic inorganics

Morphological instabilities of the InAs/GaAs(001) interface and their effect on the self-assembling of InAs quantum-dot arrays

F. Patella, F. Arciprete, E. Placidi, S. Nufris, M. Fanfoni, A. Sgarlata, D. Schiumarini, and A. Balzarotti

Appl. Phys. Lett. 81, 2270 (2002); http://dx.doi.org/10.1063/1.1508416 (3 pages) | Cited 12 times

Online Publication Date: 9 September 2002

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The morphology of the InAs/GaAs(001) system has been imaged by atomic force microscopy (AFM) at different stages of the epitaxial growth from the initial formation of a pseudomorphic two-dimensional (2D) interace up to the self-aggregation of InAs quantum dots (QDs). The substrate texture and the dependence of the cation diffusion on the elastic strain field fully control the lateral ordering of the nanoparticles in the self assembling process and determine the final morphology of multistacked InAs QD arrays. © 2002 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
68.37.Ps Atomic force microscopy (AFM)
81.05.Ea III-V semiconductors
68.35.Fx Diffusion; interface formation
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation

Tunnel barrier formation using argon-ion irradiation and single quantum dots in multiwall carbon nanotubes

M. Suzuki, K. Ishibashi, K. Toratani, D. Tsuya, and Y. Aoyagi

Appl. Phys. Lett. 81, 2273 (2002); http://dx.doi.org/10.1063/1.1507608 (3 pages) | Cited 30 times

Online Publication Date: 9 September 2002

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Argon-ion irradiation has been used to form a tunnel barrier in multiwall carbon nanotubes and single quantum dots have been fabricated with this technique. The periodic Coulomb diamonds have been shown at 10 K and the periodic Coulomb oscillations have been observed up to around 80 K. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
61.82.Rx Nanocrystalline materials
61.80.Jh Ion radiation effects
85.35.Kt Nanotube devices
81.07.Ta Quantum dots

High structural order in thin films of the organic semiconductor diindenoperylene

A. C. Dürr, F. Schreiber, M. Münch, N. Karl, B. Krause, V. Kruppa, and H. Dosch

Appl. Phys. Lett. 81, 2276 (2002); http://dx.doi.org/10.1063/1.1508436 (3 pages) | Cited 57 times

Online Publication Date: 9 September 2002

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We report extraordinary structural order along the surface normal in thin films of the organic semiconductor diindenoperylene (DIP) deposited on silicon–dioxide surfaces. Cross-sectional transmission electron microscopy (TEM), noncontact atomic force microscopy (NC–AFM), as well as specular and diffuse x-ray scattering measurements were performed to characterize thin films of DIP. Individual monolayers of essentially upright-standing DIP molecules could be observed in the TEM images indicative of high structural order. NC–AFM images showed large terraces with monomolecular steps of ≈ 16.5 Å height. Specular DIP Bragg reflections up to high order with Laue oscillations confirmed the high structural order. A semi-kinematic fit to the data allowed a precise determination of the oscillatory DIP electron density ρel.,DIP(z). The mosaicity of the DIP thin films was obtained to be smaller than 0.01°. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.70.Ck X-ray scattering
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X-ray standing wave microscopy: Chemical microanalysis with atomic resolution

Michael Drakopoulos, Jörg Zegenhagen, Anatoly Snigirev, Irina Snigireva, Maik Hauser, Karl Eberl, Vitalii Aristov, Leonid Shabelnikov, and Vecheslav Yunkin

Appl. Phys. Lett. 81, 2279 (2002); http://dx.doi.org/10.1063/1.1506779 (3 pages) | Cited 12 times

Online Publication Date: 9 September 2002

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We introduce a microprobe technique based on the x-ray standing wave method (XSW) demonstrating that structural analysis can be achieved with chemical sensitivity on a microscopic scale. We apply this XSW microscopy technique to study an epitaxially grown GaAs/Al0.1Ga0.9As/GaAs(001) heterostructure in cross section. We focus the x-ray beam by a refractive lens onto the cleaved sample and analyze the constituent elements within the 4 μm thick Al0.1Ga0.9As layer resolving the substitutional location of Al. The new micro-XSW technique will permit microscopic examinations of the structure of integrated semiconductor devices or microscopic crystalline grains with chemical sensitivity and structural resolution on the pm scale. © 2002 American Institute of Physics.
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07.85.Tt X-ray microscopes
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.37.Yz X-ray microscopy
68.65.Ac Multilayers

Laser-induced surface potential transients observed in III-nitride heterostructures

G. Koley, Ho-Young Cha, C. I. Thomas, and M. G. Spencer

Appl. Phys. Lett. 81, 2282 (2002); http://dx.doi.org/10.1063/1.1506416 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2002

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We report on very long surface potential transients induced by ultraviolet laser illumination, which have been observed in nitride heterostructures. These surface potential transients correlate with current transients when measured simultaneously. Under illumination, electron–hole pairs are generated, which screen the electric field in the AlGaN barrier layer causing the surface potential to decrease. The holes move toward the surface assisted by the electric field in the AlGaN while the electrons increase the sheet charge concentration at the AlGaN/GaN interface, decreasing the net charge dipole across the barrier layer. This reduction can cause the surface potential to vary as much as 1 V between the unilluminated and illuminated states. The long transient response observed after the laser is turned off is explained by the slow recombination of the holes with the electrons thermionically emitted from the potential well at the interface. The thermionic emission is modeled by a continuously varying barrier potential, which results in a stretched exponential-type response. © 2002 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
73.20.At Surface states, band structure, electron density of states
73.25.+i Surface conductivity and carrier phenomena
79.40.+z Thermionic emission
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects

Bright electroluminescence from a conjugated dendrimer

Dongge Ma, J. M. Lupton, I. D. W. Samuel, Shi-Chun Lo, and P. L. Burn

Appl. Phys. Lett. 81, 2285 (2002); http://dx.doi.org/10.1063/1.1507826 (3 pages) | Cited 15 times

Online Publication Date: 9 September 2002

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Photoluminescence and electroluminescence (EL) from a conjugated dendrimer consisting of three distyrylbenzene units linked by a central nitrogen atom as core and meta-linked biphenyl units as dendrons were investigated. The conjugated dendrimer emits green light and shows photoluminescence quantum efficiency of 9%. Bright electroluminescence was realized by using bilayer devices with blurred interface, which were fabricated by sequentially spin coating a neat dendrimer and a dendrimer doped with 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). The devices have the following structure: indium tin oxide/3,4-polyethylenedioxythiothene-polystyrenesulfonate/dendrimer/ dendrimer:PBD/Al. By optimizing the concentration of PBD, the maximum brightness and EL quantum efficiency reach 4100 cd/m2 and 0.17%, respectively. This is the best result reported so far on organic light-emitting diodes using dendrimer as an active material with an Al cathode. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
42.70.Jk Polymers and organics
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Dynamic higher-order correction of acoustic aberration due to material microstructure

S. D Sharples, M. Clark, and M. G. Somekh

Appl. Phys. Lett. 81, 2288 (2002); http://dx.doi.org/10.1063/1.1507827 (3 pages) | Cited 3 times

Online Publication Date: 9 September 2002

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Material microstructure, such as grains in metals, can perturb ultrasound as it propagates through—or on the surface of—the material. This acoustic aberration affects the accuracy and reliability of ultrasound measurements and is a fundamental limit to resolution for many materials. Using an all-optical approach to generation and detection of surface acoustic waves, we detect the acoustic wave front aberrations, and correct for them by calculating a different generation profile, which is imaged onto the material using a spatial light modulator. © 2002 American Institute of Physics.
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43.35.Pt Surface waves in solids and liquids
43.25.Fe Effect of nonlinearity on acoustic surface waves
68.35.Iv Acoustical properties
62.65.+k Acoustical properties of solids
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.58.Ls Acoustical lenses and microscopes
42.79.Hp Optical processors, correlators, and modulators
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.60.Qv Signal processing instrumentation, integrated systems, smart transducers, devices and architectures, displays and interfaces for acoustic systems

Near-field photoluminescence imaging of single semiconductor quantum constituents with a spatial resolution of 30 nm

K. Matsuda, T. Saiki, S. Nomura, M. Mihara, and Y. Aoyagi

Appl. Phys. Lett. 81, 2291 (2002); http://dx.doi.org/10.1063/1.1507357 (3 pages) | Cited 26 times

Online Publication Date: 9 September 2002

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High-resolution photoluminescence (PL) imaging of semiconductor quantum dots (QDs) was demonstrated using a low-temperature near-field scanning optical microscope. We systematically evaluated the spatial resolution for various fiber probes with different aperture diameters ranging from 30 to 135 nm. We achieved a spatial resolution of 30 nm ( ∼ λ/30:λ = 930 nm) in the PL imaging of self-assembled InAs QDs due to both improvement in probe preparation and optimization of the sample structure. The spatial resolution obtained in this study is on the scale of semiconductor quantum constituents and will make it possible to map out and manipulate the wave function in quantum-confined systems. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.-m Photoluminescence, properties and materials
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