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24 Jan 2005

Volume 86, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 043106 (2005); http://dx.doi.org/10.1063/1.1853514 (3 pages)

William L. Hughes and Zhong L. Wang
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Bulk synthesis and high-temperature ferromagnetism of (In1−xFex)2O3−σ with Cu co-doping

Young K. Yoo, Qizhen Xue, Hyung-Chul Lee, Shifan Cheng, X.-D. Xiang, Gerald F. Dionne, Shifa Xu, Jun He, Yong S. Chu, S. D. Preite, Samuel E. Lofland, and Ichiro Takeuchi

Appl. Phys. Lett. 86, 042506 (2005); http://dx.doi.org/10.1063/1.1854720 (3 pages) | Cited 61 times

Online Publication Date: 21 January 2005

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The synthesis and magnetic properties of (In1−xFex)2O3−σ bulk ceramics with Cu co-doping are reported. Magnetic Fe ions are found to have high thermodynamic solubility (up to 20%) in the In2O3 host compound. The lattice constant decreases almost linearly as Fe doping concentration increases indicating the incorporation of Fe ions into the host lattice. The samples with high Fe concentration annealed under Ar reduced atmosphere were found to be ferromagnetic, and the Curie temperature is around 750 K. The extensive structural and magnetic studies rule out the possibility that the observed magnetism is derived from magnetic impurity phases.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.up Other materials
61.72.S- Impurities in crystals
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.30.Hx Magnetic impurity interactions
61.72.Cc Kinetics of defect formation and annealing
61.66.Fn Inorganic compounds

Magnetization step and spin reorientation in Pr5/8Ca3/8MnO3 manganites

Guixin Cao, Jincang Zhang, Shixun Cao, Chao Jing, and Xuechu Shen

Appl. Phys. Lett. 86, 042507 (2005); http://dx.doi.org/10.1063/1.1852710 (3 pages) | Cited 7 times

Online Publication Date: 21 January 2005

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The structural, magnetic, and transport properties of Pr5/8Ca3/8MnO3 single crystals with a phase-separated characteristic were systematically studied. One steplike charge-ordered antiferromagnetic-ferromagnetic transition was found below 60 K when a magnetic field of only several teslas was applied, and the step in the M-H curve became ultrasharp below 4.2 K. Here, the given charge/orbital ordering and spin structure indicated that the energy difference between ferromagnetic and charge ordering was small for Pr5/8Ca3/8MnO3. According to the model of spin and orbital coupling, the steps should be the result of spin reorientation under the magnetic field. Above 10 K, however, the step was not sharp, which was caused by thermal fluctuation and then affects the fluctuation rate of orbit.
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75.50.Dd Nonmetallic ferromagnetic materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.40.Mg Numerical simulation studies
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Ds Spin waves
75.10.Dg Crystal-field theory and spin Hamiltonians
71.45.-d Collective effects
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A possible mechanism of anomalous shift and asymmetric hysteresis behavior of ferroelectric thin films

C. K. Wong and F. G. Shin

Appl. Phys. Lett. 86, 042901 (2005); http://dx.doi.org/10.1063/1.1853520 (3 pages) | Cited 15 times

Online Publication Date: 18 January 2005

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We studied theoretically the hysteresis behavior of ferroelectric thin films. The anomalous ferroelectric response is discussed by use of a bilayer model. Electrical conductivities of the films have been taken into account. To model the effects of the inhomogeneity of polarization and permittivity across the interface, the film is assumed to possess a secondary dielectric∕ferroelectric phase (a dead or passive layer) with asymmetric conductivity. This configuration is found to produce large shifting (along the field axis) and deformation of the measured hysteresis loop. This is a manifestation of the asymmetric conductivity of the material. Theoretical calculation based on this model shows that the observed phenomena of shifted and skewed hysteresis loop in ferroelectric thin films can be explained in this way.
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77.55.-g Dielectric thin films
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.Dj Domain structure; hysteresis
68.60.Bs Mechanical and acoustical properties
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Si Segregation into Pr2O3 and La2O3 high-k gate oxides

G. Lippert, J. Dąbrowski, V. Melnik, R. Sorge, Ch. Wenger, P. Zaumseil, and H.-J. Müssig

Appl. Phys. Lett. 86, 042902 (2005); http://dx.doi.org/10.1063/1.1853521 (3 pages) | Cited 17 times

Online Publication Date: 18 January 2005

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Pr and La oxide thin films were investigated in the context of their application as high-k dielectrics in complementary metal oxide technology. The films were deposited by molecular beam epitaxy on bare and TiN-covered Si(001). The influence of growth and post-deposition annealing on the composition and electrical parameters was studied. We observed Si penetration from bare Si(001) into the growing film. Based on the results of capacitance–voltage measurements and ab initio calculations, we conclude that Si is a source of defects responsible for leakage currents.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.35.Dv Composition, segregation; defects and impurities
66.30.J- Diffusion of impurities
77.22.Ch Permittivity (dielectric function)
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing

Three-dimensional polarization imaging of (Ba,Sr)TiO3:MgO composites

Patrick Irvin, Jeremy Levy, Ruyan Guo, and Amar Bhalla

Appl. Phys. Lett. 86, 042903 (2005); http://dx.doi.org/10.1063/1.1854722 (3 pages) | Cited 15 times

Online Publication Date: 18 January 2005

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The dielectric tuning and loss of (Ba,Sr)TiO3:MgO bulk composites depend strongly on the connectivity and interaction among the two phases. To investigate this relationship, the polar structure and dynamics of these composites are mapped as a function of space and time using a pair of three-dimensional probes: second-harmonic confocal scanning optical microscopy (SH-CSOM), which maps ferroelectric polarization in three dimensions, and time-resolved scanning optical microscopy (TR-CSOM), which maps polarization dynamics along two spatial dimensions and one time dimension. SH-CSOM measurements reveal a high degree of homogeneity within the (Ba,Sr)TiO3 regions, while TR-CSOM measurements indicate that topologically connected regions respond with a spatially uniform phase.
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77.84.Lf Composite materials
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)

Hybrid titanium–aluminum oxide layer as alternative high-k gate dielectric for the next generation of complementary metal–oxide–semiconductor devices

O. Auciello, W. Fan, B. Kabius, S. Saha, J. A. Carlisle, R. P. H. Chang, C. Lopez, E. A. Irene, and R. A. Baragiola

Appl. Phys. Lett. 86, 042904 (2005); http://dx.doi.org/10.1063/1.1856137 (3 pages) | Cited 39 times

Online Publication Date: 20 January 2005

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Research is focused on finding reliable high-dielectric constant (k) oxides with high capacitance and all critical properties required for the next generation of complementary metal–oxide–semiconductor (CMOS) gates. A trade-off between dielectric constant and band-offset height is generally observed on gate oxides. Combining TiO2 and Al2O3, with the two extremes of high permittivity (k) and high band offset, we produced a TixAl1−xOy (TAO) oxide layer with k = ∼ 30 and low dielectric leakage for a next generation of high-k dielectric gates. We developed a low temperature oxidation process, following room temperature sputter-deposition of TiAl layers, to produce ultrathin TAO layers on Si with subatomic or no SiO2 or silicide interface formation. We demonstrated TAO layers with <0.5 nm equivalent oxide thickness on Si and thermal stability under rapid thermal annealing up to about 950 °C. The data presented here provide insights into fundamental physics and materials science of the TAO layer and its potential application as gate dielectric for the next generation of CMOS devices.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.65.Mq Oxidation
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
77.22.Ch Permittivity (dielectric function)
68.60.Dv Thermal stability; thermal effects
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

(Pb,La)TiO3/(Pb,Ca)TiO3 ferroelectric heterostructures for nonvolatile memories

Rosalía Poyato, M. Lourdes Calzada, and Lorena Pardo

Appl. Phys. Lett. 86, 042905 (2005); http://dx.doi.org/10.1063/1.1853506 (3 pages) | Cited 4 times

Online Publication Date: 21 January 2005

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The existence of voltage shifts in the ferroelectric loops measured in (Pb,La)TiO3/(Pb,Ca)TiO3 heterostructures onto Si-based substrates after poling at 150 °C has been studied. Results have been compared with the measured ones in (Pb,La)TiO3 and (Pb,Ca)TiO3 single-component films, which have been prepared in identical conditions. Lower voltage shifts have been obtained in the heterostructures. The reduced number of VO–VPb defect-dipoles present in the heterostructures as a consequence of the mechanism of stress relaxation via plastic deformation through vacancies diffusion that takes place in these films results in a reduced electron trapping, and thus, in a lower voltage shift of the loop.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
66.30.Lw Diffusion of other defects
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
77.55.-g Dielectric thin films
81.40.Lm Deformation, plasticity, and creep
61.72.J- Point defects and defect clusters
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.60.Bs Mechanical and acoustical properties

Piezoelectric ultrathin BaTiO3 films

Y. Drezner, M. Nitzani, and S. Berger

Appl. Phys. Lett. 86, 042906 (2005); http://dx.doi.org/10.1063/1.1857084 (3 pages) | Cited 4 times

Online Publication Date: 21 January 2005

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Ultrathin (about 3 nm thick) BaTiO3 films were deposited by rf sputtering on a Si(100) substrate. LaNiO3 thin films were used as bottom and top conductive electrodes. The BaTiO3 films show piezoelectric behavior characterized by a coefficient d31 = −1.8 pC/N. The BaTiO3 films have an extremely high resistance to electrical breakdown up to a field of about 200 MV/cm.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Jp Dielectric breakdown and space-charge effects
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Evidence of double layer quantum dot formation in a silicon-on-insulator nanowire transistor

K. H. Cho, B. H. Choi, S. H. Son, S. W. Hwang, D. Ahn, B.-G. Park, B. Naser, J.-F. Lin, and J. P. Bird

Appl. Phys. Lett. 86, 043101 (2005); http://dx.doi.org/10.1063/1.1854738 (3 pages) | Cited 3 times

Online Publication Date: 18 January 2005

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We report the observation of a unique example of double-dot transport in a silicon-on-insulator nanowire transistor. The transport at low temperature showed typical characteristics of two parallel quantum dots, and anomalous secondary minima were also observed in the dID/dVDS spectrum. Our transport data, including these secondary minima, were consistent with two parallel quantum dots, each formed at the front and at the back interface.
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85.35.Gv Single electron devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Kv Quantum dots
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.23.Hk Coulomb blockade; single-electron tunneling

Direct visualization of nanopatterns by single-molecule imaging

Erwen Mei, Alexey Sharonov, James H. Ferris, and Robin M. Hochstrasser

Appl. Phys. Lett. 86, 043102 (2005); http://dx.doi.org/10.1063/1.1850608 (3 pages) | Cited 1 time

Online Publication Date: 18 January 2005

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The structures of patterned surface regions were clearly visualized by superimposing a series of single-molecule images from a total internal reflection fluorescence microscope, clearly demonstrating that a single-molecule imaging method can be used to directly visualize nanostructures. The pattern was fabricated on a microscope cover glass that formed a sandwich with a regular cover glass. The incorporated solution of fluorescent probe dyes was examined by single-molecule techniques. The effect of the surface pattern on the diffusion of the probe has also been examined.
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87.15.M- Spectra of biomolecules
87.15.B- Structure of biomolecules
87.15.Vv Diffusion

Near-field optical spectroscopy and microscopy of self-assembled GaN/AlN nanostructures

A. Neogi, B. P. Gorman, H. Morkoç, T. Kawazoe, and M. Ohtsu

Appl. Phys. Lett. 86, 043103 (2005); http://dx.doi.org/10.1063/1.1851005 (3 pages) | Cited 5 times

Online Publication Date: 19 January 2005

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The spatial distribution and emission properties of small clusters of GaN quantum dots in an AlN matrix are studied using high-resolution electron and optical microscopy. High-resolution transmission electron microscopy reveals near vertical correlation among the GaN dots due to a sufficiently thin AlN spacer layer thickness, which allows strain induced stacking. Scanning electron and atomic force microscopy show lateral coupling due to a surface roughness of ∼ 50–60 nm. Near-field photoluminescence in the illumination mode (both spatially and spectrally resolved) at 10 K revealed emission from individual dots, which exhibits size distribution of GaN dots from localized sites in the stacked nanostructure. Strong spatial localization of the excitons is observed in GaN quantum dots formed at the tip of self-assembled hexagonal pyramid shapes with six [10mathmath] facets.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
78.55.Cr III-V semiconductors

Revised plane wave method for dispersive material and its application to band structure calculations of photonic crystal slabs

Shouyuan Shi, Caihua Chen, and Dennis W. Prather

Appl. Phys. Lett. 86, 043104 (2005); http://dx.doi.org/10.1063/1.1855425 (3 pages) | Cited 26 times

Online Publication Date: 19 January 2005

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In this letter we present a revised formulation of the plane wave method (PWM) for the band structure calculation of photonic crystals. In comparison to the conventional PWM, the formulation in this letter allows for modeling of dispersive material. One application of the presented method is for band structure calculations of photonic crystal slabs. While a thin photonic crystal slab is considered, a full three-dimensional (3D) problem can be reduced to a two-dimensional one by using the effective index method. However, the obtained effective index of such a slab is frequency dependent. The revised PWM is then applied to solve this problem. The results obtained using this algorithm have been compared with those using a full 3D finite-difference time-domain method and found to agree very well.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Self-aligned Co nanoparticle chains supported by single-crystalline Al2O3/NiAl(100) template

Wen-Chin Lin, Chien-Cheng Kuo, Meng-Fan Luo, Ker-Jar Song, and Minn-Tsong Lin

Appl. Phys. Lett. 86, 043105 (2005); http://dx.doi.org/10.1063/1.1855410 (3 pages) | Cited 20 times

Online Publication Date: 19 January 2005

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We present Co nanoparticle chains grown by vapor deposition over a single-crystalline Al2O3 layers on NiAl(100) with such features as self-limiting size distribution with the average size of ∼ 2.7 nm, well-ordered alignment, and high thermal stability. We attribute these features to peculiar one-dimensional long stripes with ∼ 4 nm interdistance on the surface of the ultrathin Al2O3 template. This nanostructure may open the door to numerous applications, such as catalysis and nanostorage, where large area well-ordered nanodots are desired.
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61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Controlled synthesis and manipulation of ZnO nanorings and nanobows

William L. Hughes and Zhong L. Wang

Appl. Phys. Lett. 86, 043106 (2005); http://dx.doi.org/10.1063/1.1853514 (3 pages) | Cited 35 times

Online Publication Date: 19 January 2005

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An experimental procedure is presented for the controlled synthesis and manipulation of ZnO nanorings and nanobows at high purity and large yield. Atomic force microscopy manipulation of the nanostructures demonstrates their mechanical toughness and flexibility. Extensive bending of the nanorings and nanobows suggests an extremely high deformation limit with the potential for building ultrasensitive electromechanical coupled nanoscale sensors, transducers, and resonators.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
68.37.Ps Atomic force microscopy (AFM)
68.35.Gy Mechanical properties; surface strains
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.16.Ta Atom manipulation

Plasma deposition of thin carbonfluorine films on aligned carbon nanotube

Peng He, Donglu Shi, Jie Lian, L. M. Wang, Rodney C. Ewing, Wim van Ooij, W. Z. Li, and Z. F. Ren

Appl. Phys. Lett. 86, 043107 (2005); http://dx.doi.org/10.1063/1.1846957 (3 pages) | Cited 4 times

Online Publication Date: 19 January 2005

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The thin film of carbonfluorine was deposited on the surfaces of aligned carbon nanotubes using a plasma polymerization treatment. High-resolution transmission electron microscopy images revealed that a thin film of the polymer layer (20 nm) was uniformly deposited on the surfaces of the aligned carbon nanotubes. Time-of-flight secondary ion mass spectroscopy and Fourier transform infrared experiments identified the carbonfluorine thin films on the carbon nanotubes. The plasma deposition mechanism is discussed.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics
61.46.-w Structure of nanoscale materials
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Rt Time of flight mass spectrometry
68.37.Lp Transmission electron microscopy (TEM)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.35.Gh Polymers on surfaces; adhesion
78.66.Qn Polymers; organic compounds

Effectiveness of TiN porous templates on the reduction of threading dislocations in GaN overgrowth by organometallic vapor-phase epitaxy

Y. Fu, Y. T. Moon, F. Yun, Ü. Özgür, J. Q. Xie, S. Doğan, H. Morkoç, C. K. Inoki, T. S. Kuan, Lin Zhou, and David J. Smith

Appl. Phys. Lett. 86, 043108 (2005); http://dx.doi.org/10.1063/1.1849833 (3 pages) | Cited 35 times

Online Publication Date: 21 January 2005

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We report on the reduction of threading dislocations in GaN overlayers grown by organometallic vapor phase epitaxy on micro-porous TiN networks. These networks were obtained by in situ annealing of thin Ti layers deposited in a metalization chamber, on the (0001) face of GaN templates. Observations by transmission electron microscopy indicate dislocation reduction by factors of up to 10 in GaN layers grown on TiN networks compared with the control GaN. X-ray diffraction shows that GaN grown on the TiN network has a smaller (102) plane peak width (4.6 arcmin) than the control GaN (7.8 arcmin). In low temperature photoluminescence spectra, a narrow excitonic full-width-at-half-maximum of 2.4 meV was obtained, as compared to 3.0 meV for the control GaN, confirming the improved crystalline quality of the overgrown GaN layers.
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81.05.Ea III-V semiconductors
81.05.Rm Porous materials; granular materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.66.Fd III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
61.43.Gt Powders, porous materials
78.55.Mb Porous materials
78.66.Nk Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Cc Kinetics of defect formation and annealing
71.35.-y Excitons and related phenomena
68.37.Lp Transmission electron microscopy (TEM)

Controlled fabrication of nanogaps in ambient environment for molecular electronics

D. R. Strachan, D. E. Smith, D. E. Johnston, T.-H. Park, Michael J. Therien, D. A. Bonnell, and A. T. Johnson

Appl. Phys. Lett. 86, 043109 (2005); http://dx.doi.org/10.1063/1.1857095 (3 pages) | Cited 91 times

Online Publication Date: 21 January 2005

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We have developed a controlled and highly reproducible method of making nanometer-spaced electrodes using electromigration in ambient lab conditions. This advance will make feasible single molecule measurements of macromolecules with tertiary and quaternary structures that do not survive the liquid-helium temperatures at which electromigration is typically performed. A second advance is that it yields gaps of desired tunneling resistance, as opposed to the random formation at liquid-helium temperatures. Nanogap formation occurs through three regimes: First it evolves through a bulk-neck regime where electromigration is triggered at constant temperature, then to a few-atom regime characterized by conductance quantum plateaus and jumps, and finally to a tunneling regime across the nanogap once the conductance falls below the conductance quantum.
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81.07.Nb Molecular nanostructures
81.16.Nd Micro- and nanolithography
66.30.Qa Electromigration
73.63.-b Electronic transport in nanoscale materials and structures
61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.40.Gk Tunneling

Giant barrier layer capacitance effects in the lithium ion conducting material La0.67Li0.25Ti0.75Al0.25O3

Susana García-Martín, Ainhoa Morata-Orrantia, Myriam H. Aguirre, and Miguel Á. Alario-Franco

Appl. Phys. Lett. 86, 043110 (2005); http://dx.doi.org/10.1063/1.1852717 (3 pages) | Cited 9 times

Online Publication Date: 21 January 2005

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High dielectric permittivity (ε′ ∼ 500 000) has been observed in polycrystalline samples of La0.67Li0.25Ti0.75Al0.25O3 over a large frequency range ( ∼ 10<f< ∼ 103 Hz) and different temperatures. Complex impedance spectroscopy measurements demonstrate that the origin of the high dielectric constant can be attributed to a barrier layer capacitor associated with grain boundary effects in the ion conducting material.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.Mm Grain and twin boundaries
82.80.Fk Electrochemical methods
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High-photosensitivity p-channel organic phototransistors based on a biphenyl end-capped fused bithiophene oligomer

Yong-Young Noh, Dong-Yu Kim, Yuji Yoshida, Kiyoshi Yase, Byung-Jun Jung, Eunhee Lim, and Hong-Ku Shim

Appl. Phys. Lett. 86, 043501 (2005); http://dx.doi.org/10.1063/1.1856144 (3 pages) | Cited 63 times

Online Publication Date: 18 January 2005

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We report highly photosensitive organic phototransistors (OPTs) based on a 2,5-bis-biphenyl-4-yl-thieno[3,2-b]thiophene (BPTT). The measured maximum sensitivity and the ratio of photocurrent to dark current (Iph/Idark) in BPTT OPTs were 82 A/W and 2.0×105 under 380 nm UV light with 1.55 mW/cm2, respectively. The prepared OPTs show a photocurrent response similar to the absorption spectrum of BPTT. The major mechanisms for photocurrent amplification in this device were verified from experimental results as photovoltaic (turn-on) and photocurrent effect (turn-off) by a fitting to theoretic equations.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Tv Field effect devices
73.50.Pz Photoconduction and photovoltaic effects
61.82.Fk Semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
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Mechanical perturbation-induced fluorescence change of green fluorescent protein

Takashi Kodama, Hiroyuki Ohtani, Hideo Arakawa, and Atsushi Ikai

Appl. Phys. Lett. 86, 043901 (2005); http://dx.doi.org/10.1063/1.1856142 (3 pages) | Cited 13 times

Online Publication Date: 20 January 2005

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The force curve measurement mode of the atomic force microscope (AFM) is a powerful experimental technique in biotechnology. However, it is more effective if the spectroscopic properties of the biomolecule in the contact area can be simultaneously measured. Thus, we developed a confocal laser scanning microscope/AFM system. In this study, we simultaneously measured the fluorescence spectra of green fluorescent protein with the application of an external force in order to investigate the stability and dynamics of the β-barrel structure. Consequently, the fluorescence was quenched by applying both compression and extension forces and the quenching efficiencies differed in each case.
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87.80.-y Biophysical techniques (research methods)
07.79.Lh Atomic force microscopes
87.14.E- Proteins
87.64.Dz Scanning tunneling and atomic force microscopy
87.15.M- Spectra of biomolecules
87.15.H- Dynamics of biomolecules
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Miniature quantum-well microwave spectrometer operating at liquid-nitrogen temperatures

I. V. Kukushkin, S. A. Mikhailov, J. H. Smet, and K. von Klitzing

Appl. Phys. Lett. 86, 044101 (2005); http://dx.doi.org/10.1063/1.1856143 (3 pages) | Cited 15 times

Online Publication Date: 18 January 2005

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We demonstrate that a two-dimensional electron system fabricated from a GaAs/AlGaAs quantum well in the presence of a magnetic field B possesses the ability to detect electromagnetic radiation in a broad frequency range. Irradiation of the sample with microwaves produces a dc-photovoltage which oscillates as a function of B. The amplitude and the period of the oscillations are proportional to the radiation power and the wavelength, respectively. Successful operation of such a detector∕spectrometer is reported for microwave frequencies up to ∼ 150 GHz and temperatures up to ∼ 80 K. We do not anticipate any principal difficulties in extending the operation frequency further into the terahertz region.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.21.Fg Quantum wells

Multiple-spot parallel processing for laser micronanofabrication

Jun-ichi Kato, Nobuyuki Takeyasu, Yoshihiro Adachi, Hong-Bo Sun, and Satoshi Kawata

Appl. Phys. Lett. 86, 044102 (2005); http://dx.doi.org/10.1063/1.1855404 (3 pages) | Cited 64 times

Online Publication Date: 18 January 2005

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A tightly focused femtosecond laser has been established as a unique tool for micronanostructure fabrication due to its intrinsic three-dimensional processing. In this letter, we utilize a microlens array to produce multiple spots for parallel fabrication, giving rise to a revolutionary augmentation for our previously developed single-beam two-photon photopolymerization technology [ S. Kawata, H.-B. Sun, T. Tanaka, and K. Takada, Nature (London) 412, 697 (2001) ]. Two- and three-dimensional multiple structures, such as microletter set and self-standing microspring array, are demonstrated as examples of mass production. More than 200 spot simultaneous fabrication has been realized by optimizing the exposure condition for the photopolymerizable resin, i.e., a two-order increase of yield efficiency. Potential applications of this technique are discussed.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.62.-b Laser applications
42.79.Bh Lenses, prisms and mirrors
81.16.-c Methods of micro- and nanofabrication and processing
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Jk Polymers and organics

Electron trapping and detrapping in ion-beam-damaged diamond surfaces

A. Hoffman, I. Andrienko, D. N. Jamieson, and S. Prawer

Appl. Phys. Lett. 86, 044103 (2005); http://dx.doi.org/10.1063/1.1852083 (3 pages) | Cited 10 times

Online Publication Date: 19 January 2005

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Ion-beam-damaged diamond surfaces subjected to electron irradiation are observed to develop a pronounced negative surface charge. In this study, this effect is shown to be associated with the capture of electrons into traps created by the ion irradiation process. The trapped charge increases with ion dose and incident electron current, and decreases with increasing sample temperature and laser illumination as the traps are depleted of charge. An activation energy for detrapping of about 1.5 eV is deduced from the temperature dependence of the charging.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
71.55.Ht Other nonmetals
61.82.Ms Insulators
61.80.Jh Ion radiation effects
61.80.Fe Electron and positron radiation effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Application of inverse problems to current density reconstruction inside components

T. Talbert, L. Nativel, T. Martiré, S. Faucher, Ch. Joubert, and N. Daudé

Appl. Phys. Lett. 86, 044104 (2005); http://dx.doi.org/10.1063/1.1849411 (3 pages)

Online Publication Date: 20 January 2005

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In this letter, a nonintrusive method to retrieve current density inside a component is presented. Numerous applications including passive component reliability tests are concerned. The method based upon the measurement of the electromagnetic field radiated by the component is used to reconstruct the current distribution by means of inverse problem methodology. It is applied to the simple case of a small wire loop in order to validate the measurement system (magnetic near-field) and the reconstruction method.
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07.55.Db Generation of magnetic fields; magnets
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Highly sensitive time-of-flight secondary-ion mass spectroscopy for contaminant analysis of semiconductor surface using cluster impact ionization

K. Hirata, Y. Saitoh, A. Chiba, K. Narumi, Y. Kobayashi, and Y. Ohara

Appl. Phys. Lett. 86, 044105 (2005); http://dx.doi.org/10.1063/1.1852715 (3 pages) | Cited 4 times

Online Publication Date: 21 January 2005

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To compare emission yields of secondary ions from contaminated silicon wafers between cluster and monoatomic ion impacts, pulsed C1+ and C8+ beams are applied to time-of-flight secondary-ion mass spectrometry. C8+ impact of 0.5 MeV/atom provides higher secondary-ion emission yields per incident atom than C1+ impact of 0.5 MeV/atom for organic and metallic contaminants. Higher peak intensities are also observed for a C8+ ion beam with a reduced energy. The enhanced emission yields of secondary ions originating from the contaminants show that mass spectrometry with cluster impact ionization is a powerful analytical tool for highly sensitive detection of the surface contaminants on the silicon wafers.
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82.80.Rt Time of flight mass spectrometry
68.47.Fg Semiconductor surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.-b Surface treatments
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