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29 Jul 2002

Volume 81, Issue 5, pp. 789-944

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Current-controlled bi-stable domain configurations in Ni81Fe19 elements: An approach to magnetic memory devices

H. Koo, C. Krafft, and R. D. Gomez

Appl. Phys. Lett. 81, 862 (2002); http://dx.doi.org/10.1063/1.1495883 (3 pages) | Cited 31 times

Online Publication Date: 22 July 2002

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The discovery of current-switchable bi-stable remanent domain configurations on small ferromagnetic islands is reported. Rectangular NiFe islands with a thickness of 50 to 100 nm and lateral dimensions on the order of several microns were imaged using magnetic force microscopy after application of 10 ns current pulses through the material. The closure configuration can be set into either the 4 or 7 domain configuration by applying positive or negative current polarity at density on the order 107 A/cm2. The chirality of the closure patterns is fixed, implying that only two rather than four states are stable in these patterns. The possibility of using these configurations as a means of storing a logic state for memory applications is discussed. © 2002 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys

High resolution magnetic force microscopy using focused ion beam modified tips

G. N. Phillips, M. Siekman, L. Abelmann, and J. C. Lodder

Appl. Phys. Lett. 81, 865 (2002); http://dx.doi.org/10.1063/1.1497434 (3 pages) | Cited 36 times

Online Publication Date: 22 July 2002

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Atomic force microscope tips coated by the thermal evaporation of a magnetic 30 nm thick Co film have been modified by focused ion beam milling with Ga+ ions to produce tips suitable for magnetic force microscopy. Such tips possess a planar magnetic element with high magnetic shape anisotropy, an extremely high aspect ratio of greater than 30:1, and an end radius of less than 25 nm. These tips have been used in a commercial atomic force microscope under ambient conditions to obtain 30 nm resolution magnetic images of an established CoNi/Pt multilayer reference sample. © 2002 American Institute of Physics.
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07.79.Pk Magnetic force microscopes
07.79.Lh Atomic force microscopes
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy

Very high trapped fields in neutron irradiated and reinforced YBa2Cu3O7−δ melt-textured superconductors

R. Gonzalez-Arrabal, M. Eisterer, H. W. Weber, G. Fuchs, P. Verges, and G. Krabbes

Appl. Phys. Lett. 81, 868 (2002); http://dx.doi.org/10.1063/1.1497705 (3 pages) | Cited 9 times

Online Publication Date: 22 July 2002

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We report on very high trapped fields (13.3 T at 33 K) achieved in bulk YBa2Cu3O7−δ melt-textured monoliths, which were reinforced by steel tubes to compensate the tensile stress generated during activation. The flux pinning properties were improved by neutron irradiation. The resulting increase of the critical current density shifts the maximum attainable trapped fields to higher temperatures (by about 10 K). © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
61.80.Hg Neutron radiation effects
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.62.Dh Effects of crystal defects, doping and substitution

Surface-modified GaAs terahertz plasmon emitter

J. Darmo, G. Strasser, T. Müller, R. Bratschitsch, and K. Unterrainer

Appl. Phys. Lett. 81, 871 (2002); http://dx.doi.org/10.1063/1.1497192 (3 pages) | Cited 8 times

Online Publication Date: 22 July 2002

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We studied the THz emission from n-GaAs plasmon emitters modified by low-temperature-grown (LT) GaAs surface layers. The THz emission is increased since the LT GaAs pins the Fermi level at a midgap position, increasing the surface depletion field. For a THz emitter with a 70-nm-thick LT GaAs layer we observe without external fields a THz emission intensity of 140 nW. In addition, the long-term performance of the modified emitters is improved by the LT GaAs surface layer. © 2002 American Institute of Physics.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.20.At Surface states, band structure, electron density of states
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
81.65.Mq Oxidation

Intrinsic nanostructural domains: Possible origin of weaklinkless superconductivity in the quenched reaction product of Mg and amorphous B

S. Li, O. Prabhakar, T. T. Tan, C. Q. Sun, X. L. Wang, S. Soltanian, J. Horvat, and S. X. Dou

Appl. Phys. Lett. 81, 874 (2002); http://dx.doi.org/10.1063/1.1497712 (3 pages) | Cited 6 times

Online Publication Date: 22 July 2002

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Smooth modulation structure of Mg–B alloy in the quenched reaction product of Mg and amorphous B was studied. It indicates that the MgB2 formed possibly in spinodal decomposition, thus resulting in MgB2 nanodomains. It was found that the nanodomains with small angle boundaries of atomic-scale width were distributed within the subgrains that constitute the clusters in MgB2 grains. This nanostructural characteristic may be intrinsic in the quenched reaction product of Mg and amorphous B. It makes the nanodomain boundaries not act as barriers to the current percolation path, thus exhibiting no weak-link problem in the MgB2. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.62.Dh Effects of crystal defects, doping and substitution
74.20.Mn Nonconventional mechanisms
61.46.-w Structure of nanoscale materials
74.25.F- Transport properties
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Strontium–titanate-doped lead metaniobate ferroelectric thin films

J. M. Xue, S. Ezhilvalavan, X. S. Gao, and J. Wang

Appl. Phys. Lett. 81, 877 (2002); http://dx.doi.org/10.1063/1.1494838 (3 pages) | Cited 3 times

Online Publication Date: 22 July 2002

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Ferroelectric polymorph of lead metaniobate (PbNb2O6) exhibits an orthorhombic structure, which is metastable at room temperature and can only be obtainable by quenching from high temperatures ( ∼ 1200 °C). In this letter, we report a ferroelectric PbNb2O6 thin film doped with SrTiO3 (Pb0.95Sr0.05(Nb2)0.98Ti0.05O6) with orthorhombic structure on Pt/Ti/Si substrate, which was prepared via a sol-gel route. The orthorhombic structure was developed at 900 °C at a normal heating rate of 5 °C/min and cooling rate of 10 °C/min. The PbNb2O6 film exhibited a remanent polarization (Pr) of 12.3 μC/cm2 and a coercive field (Ec) of 39 kV/cm, respectively, when measured at an applied field of 143 kV/cm. The leakage current density was 1.02×10−5 A/cm2 at 100 kV/cm. The room-temperature dielectric constant and dissipation factor was stable ( ∼ 325 and ∼ 1.5%, respectively) over a frequency range of 1 kHz to 1 MHz. © 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
68.55.-a Thin film structure and morphology
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Leakage current characteristics of laser-ablated SrBi2Nb2O9 thin films

Rasmi R. Das, P. Bhattacharya, W. Pérez, Ram S. Katiyar, and A. S. Bhalla

Appl. Phys. Lett. 81, 880 (2002); http://dx.doi.org/10.1063/1.1495880 (3 pages) | Cited 8 times

Online Publication Date: 22 July 2002

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We have studied the leakage current conduction mechanism of pulsed-laser-deposited SrBi2Nb2O9 (SBN) thin films on platinized silicon substrates. The time-dependent dc leakage current densities of SBN thin films do not follow Curie–von Schweidler power law. Instead the contribution of conduction current is predominantly electronic. At lower fields, the leakage current follows the ohmic behavior, and it increases exponentially for higher fields. The leakage current density of the SBN thin films was studied at elevated temperatures, and the data were fitted with the Schottky emission model. The effective Richardson’s constant was calculated to be about 8.7×10−6 A/cm2 K2. The Schottky barrier height of the SBN thin films was estimated to be 1.37 eV. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
73.30.+y Surface double layers, Schottky barriers, and work functions

Recombination-enhanced extension of stacking faults in 4H-SiC p-i-n diodes under forward bias

A. Galeckas, J. Linnros, and P. Pirouz

Appl. Phys. Lett. 81, 883 (2002); http://dx.doi.org/10.1063/1.1496498 (3 pages) | Cited 58 times

Online Publication Date: 22 July 2002

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The extension of stacking faults in a forward-biased 4H-SiC PiN diodes by the recombination-enhanced motion of leading partial dislocations has been investigated by the technique of optical emission microscopy. From the temperature dependence of the measured velocity of the partials, an activation energy of 0.27 eV is obtained. Based on this and analysis of the emission spectra, a radiative recombination level of 2.8 eV for the stacking fault, and two energy levels for the partial dislocation, a radiative one at 1.8 eV and a nonradiative at 2.2 eV, have been determined. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
61.72.Nn Stacking faults and other planar or extended defects
61.72.Lk Linear defects: dislocations, disclinations
78.60.Fi Electroluminescence
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.55.Ht Other nonmetals
73.20.Hb Impurity and defect levels; energy states of adsorbed species

From incipient ferroelectricity in CaTiO3 to real ferroelectricity in Ca1−xPbxTiO3 solid solutions

V. V. Lemanov, A. V. Sotnikov, E. P. Smirnova, and M. Weihnacht

Appl. Phys. Lett. 81, 886 (2002); http://dx.doi.org/10.1063/1.1497199 (3 pages) | Cited 21 times

Online Publication Date: 22 July 2002

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Dielectric spectra of ceramic samples of Ca1−xPbxTiO3 (0 ⩽ x ⩽ 0.4) solid solutions were studied at frequencies between 10 Hz and 1 MHz in a temperature range of 4.2–300 K. A ferroelectric phase transition was observed at x = 0.3 with transformation to a relaxor type behavior at x>0.3. The transition temperature Tc follows a linear dependence Tc∝(x−xc) with xc = 0.28 contrary to a square-root dependence Tc∝(x−xc)1/2 predicted by the theory for incipient ferroelectrics. The critical concentration essentially exceeds the xc values for SrTiO3 and KTaO3 incipient ferroelectrics. © 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.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)

Thickness-induced stabilization of ferroelectricity in SrRuO3/Ba0.5Sr0.5TiO3/Au thin film capacitors

L. J. Sinnamon, R. M. Bowman, and J. M. Gregg

Appl. Phys. Lett. 81, 889 (2002); http://dx.doi.org/10.1063/1.1496144 (3 pages) | Cited 36 times

Online Publication Date: 22 July 2002

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Pulsed-laser deposition has been used to fabricate Au/Ba0.5Sr0.5TiO3/SrRuO3/MgO thin film capacitor structures. Crystallographic and microstructural investigations indicated that the Ba0.5Sr0.5TiO3 (BST) had grown epitaxially onto the SrRuO3 lower electrode, inducing in-plane compressive and out-of-plane tensile strain in the BST. The magnitude of strain developed increased systematically as film thickness decreased. At room temperature this composition of BST is paraelectric in bulk. However, polarization measurements suggested that strain had stabilized the ferroelectric state, and that the decrease in film thickness caused an increase in remanent polarization. An increase in the paraelectric–ferroelectric transition temperature upon a decrease in thickness was confirmed by dielectric measurements. Polarization loops were fitted to Landau–Ginzburg–Devonshire (LGD) polynomial expansion, from which a second order paraelectric–ferroelectric transition in the films was suggested at a thickness of ∼500 nm. Further, the LGD analysis showed that the observed changes in room temperature polarization were entirely consistent with strain coupling in the system. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.B- Phase transitions and Curie point
68.60.Bs Mechanical and acoustical properties
77.22.Ej Polarization and depolarization

Shear-mode piezoelectric properties of Pb(Yb1/2Nb1/2)O3–PbTiO3 single crystals

Shujun Zhang, Lebrun Laurent, Sorah Rhee, Clive A. Randall, and Thomas R. Shrout

Appl. Phys. Lett. 81, 892 (2002); http://dx.doi.org/10.1063/1.1497435 (3 pages) | Cited 20 times

Online Publication Date: 22 July 2002

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In this letter, the shear-mode piezoelectric and electromechanical properties of 0.55Pb(Yb1/2Nb1/2)O3–0.45PbTiO3 (PYNT45) single crystals are reported. The piezoelectric coefficients d15 and g15 were found to be 2100 pC/N and 0.064 Vm/N, respectively, with an electromechanical coupling coefficient k15 of 91% at room temperature. With increasing temperature, the values decreased dramatically above 168 °C, corresponding to the ferroelectric–ferroelectric phase transition temperature. In contrast to 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 single crystals, PYNT45 crystals exhibit a larger g15 and the useful temperature range is significantly expanded. High-temperature aging experiments showed that PYNT45 single crystals exhibit good domain stability. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis

Ferroelectric Pb(Zr,Ti)O3/Al2O3/4H–SiC diode structures

S.-M. Koo, S. I. Khartsev, C.-M. Zetterling, A. M. Grishin, and M. Östling

Appl. Phys. Lett. 81, 895 (2002); http://dx.doi.org/10.1063/1.1497443 (3 pages) | Cited 5 times

Online Publication Date: 22 July 2002

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Pb(Zr,Ti)O3 (PZT) films (450 nm thick) were grown on 4H–silicon carbide (SiC) substrates by a pulsed-laser deposition technique. X-ray diffraction confirms single PZT phase without a preferred orientation. Stable capacitance–voltage (C–V) loops with low conductance (<0.1 mS/cm2, tan δ ∼ 0.0007 at 400 kHz) and memory window as wide as 10 V were obtained when 5-nm-thick Al2O3 was used as a high band gap (Eg ∼ 9 eV) barrier buffer layer between PZT (Eg ∼ 3.5 eV) and SiC (Eg ∼ 3.2 eV). High-frequency (400 kHz) C–V characteristics revealed clear accumulation, and depletion behavior. Although the charge injection from SiC is the dominant mechanism for C–V hysteresis in PZT/Al2O3/SiC, negligible sweep rate dependence and negligible applied bias dependence were observed compared to that of PZT/SiC. By using room-temperature photoilluminated C–V measurements, the interface states as well as the charge trapping in the PZT/Al2O3 stacks have been calculated. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
81.15.Fg Pulsed laser ablation deposition
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.50.Gk Non-volatile ferroelectric memories
71.20.Nr Semiconductor compounds

Effect of atmosphere during heating of substrate on the low temperature deposition of metalorganic chemical vapor deposited Pb(Zrx,Ti1−x)O3 thin films

Kouji Tokita, Masanori Aratani, and Hiroshi Funakubo

Appl. Phys. Lett. 81, 898 (2002); http://dx.doi.org/10.1063/1.1497446 (3 pages) | Cited 7 times

Online Publication Date: 22 July 2002

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The effect of the atmosphere during the heating of a substrate before starting the deposition on the characteristics of the deposited Pb(Zrx,Ti1−x)O3 (PZT) films was investigated. Rhombohedral PZT films were prepared on Pt/Ti/SiO2/Si substrates by metalorganic chemical vapor deposition (MOCVD) from 415 to 580 °C. PZT films with smooth surfaces and low leakage current densities were obtained when the substrate was heated under an Ar atmosphere at the heating rate of 7 °C/min. Moreover, a crystalline PZT film having good ferroelectricity was obtained at as low as 415 °C when the substrate was heated under the Ar atmosphere, while the film consisted of an amorphous phase when the substrate was heated under an O2 atmosphere. These results clearly show that heating the substrate under an Ar atmosphere before starting the deposition is effective for obtaining a film with a large ferroelectricity at a low deposition temperature for the MOCVD process. © 2002 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.80.-e Ferroelectricity and antiferroelectricity
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.40.Gh Other heat and thermomechanical treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.61.Ng Insulators
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Carbon nanotube scanning probe for profiling of deep-ultraviolet and 193 nm photoresist patterns

Cattien V. Nguyen, Ramsey M. D. Stevens, Jabulani Barber, Jie Han, M. Meyyappan, Martha I. Sanchez, Carl Larson, and William D. Hinsberg

Appl. Phys. Lett. 81, 901 (2002); http://dx.doi.org/10.1063/1.1496139 (3 pages) | Cited 31 times

Online Publication Date: 22 July 2002

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The continual scaling down of complementary metal–oxide semiconductor feature size to 100 nm and below necessitates a characterization technique to resolve high-aspect-ratio features in the nanoscale regime. We report the use of atomic force microscopy coupled with high-aspect-ratio multiwalled carbon nanotube (MWCNT) scanning probe tip for the purpose of imaging surface profile of photoresists. MWCNT tips of 5–10 nm in diameter and about a micron long are used. Their exceptional mechanical strength and ability to buckle reversibly enable resolution of steep, deep nanoscale features. Images of photoresist patterns generated by 257 nm interference lithography as well as 193 nm lithography are presented to demonstrate MWCNT scanning probe tips for applications in metrology. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
81.16.Nd Micro- and nanolithography
85.35.Kt Nanotube devices
61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
85.40.Hp Lithography, masks and pattern transfer

On the role of Ge in the growth of β-FeSi2 on silicon (100) surfaces

A. Zenkevich, P. I. Gaiduk, H. P. Gunnlaugsson, and G. Weyer

Appl. Phys. Lett. 81, 904 (2002); http://dx.doi.org/10.1063/1.1497185 (3 pages)

Online Publication Date: 22 July 2002

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The microstructure of β-FeSi2 silicide layers formed with the addition of Ge by pulsed laser deposition at 650 °C on (001) Si substrate has been investigated by transmission electron microscopy and Mössbauer spectroscopy. The Ge atoms are not incorporated in the silicide in noticeable amounts but the addition causes the growth of β-FeSi2 micrograins with a high density of specific twin lamellae, whereas Ge segregates in epitaxial SiGe alloy grains. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
68.35.Dv Composition, segregation; defects and impurities
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.72.Mm Grain and twin boundaries

Pt–WOx electrode structure for thin-film fuel cells

Kyung-Won Park, Kwang-Soon Ahn, Jong-Ho Choi, Yoon-Chae Nah, Young-Min Kim, and Yung-Eun Sung

Appl. Phys. Lett. 81, 907 (2002); http://dx.doi.org/10.1063/1.1497707 (3 pages) | Cited 26 times

Online Publication Date: 22 July 2002

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An electrode structure consisting of two phases of Pt and WOx for use in thin-film fuel cells was designed and fabricated using a cosputtering system with a Pt metal and a tungsten oxide target. The coexistence of a polycrystalline Pt nanosized phase and an amorphous tungsten oxide phase in the electrode layer was confirmed by transmission electron microscopic images and x-ray diffraction data. In addition, compared with a Pt thin-film electrode, the two-phase electrode of Pt and WOx showed excellent performance for the devices because of the improved activity of the Pt metallic phase and the spill-over effect of porous tungsten oxides. © 2002 American Institute of Physics.
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82.47.-a Applied electrochemistry
82.45.Fk Electrodes
68.55.-a Thin film structure and morphology

Electronic properties of multiwalled carbon nanotubes in an embedded vertical array

Jun Li, Ramsey Stevens, Lance Delzeit, Hou Tee Ng, Alan Cassell, Jie Han, and M. Meyyappan

Appl. Phys. Lett. 81, 910 (2002); http://dx.doi.org/10.1063/1.1496494 (3 pages) | Cited 65 times

Online Publication Date: 22 July 2002

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We demonstrate integration of carbon nanotubes into large scale vertically aligned electrode arrays, by filling the as-grown samples with conformal SiO2 using chemical vapor deposition. Subsequent mechanical polishing yields a flat surface with only the very ends of the nanotube array exposed. The electronic properties of individual carbon nanotubes in the array are measured using current-sensing atomic force microscopy. These vertical nanotube arrays are suitable for fabricating various electronic devices and sensors. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
81.07.De Nanotubes
68.37.Ps Atomic force microscopy (AFM)

Integration of suspended carbon nanotube arrays into electronic devices and electromechanical systems

Nathan R. Franklin, Qian Wang, Thomas W. Tombler, Ali Javey, Moonsub Shim, and Hongjie Dai

Appl. Phys. Lett. 81, 913 (2002); http://dx.doi.org/10.1063/1.1497710 (3 pages) | Cited 98 times

Online Publication Date: 22 July 2002

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A synthetic strategy is devised for reliable integration of long suspended single-walled carbon nanotubes into electrically addressable devices. The method involves patterned growth of nanotubes to bridge predefined molybdenum electrodes, and is versatile in yielding various microstructures comprised of suspended nanotubes that are electrically wired up. The approach affords single-walled nanotube devices without any postgrowth processing, and will find applications in scalable nanotube transistors (mobility up to 10 000 cm2/V s) and nanoelectromechanical systems based on nanowires. © 2002 American Institute of Physics.
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85.35.Kt Nanotube devices
73.63.Fg Nanotubes
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.65.+h Molecular electronic devices
81.07.De Nanotubes

Dynamic force microscopy in superfluid helium

F. D. Callaghan, X. Yu, and C. J. Mellor

Appl. Phys. Lett. 81, 916 (2002); http://dx.doi.org/10.1063/1.1496503 (3 pages) | Cited 5 times

Online Publication Date: 22 July 2002

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Piezoelectric quartz tuning forks have been used for topographic dynamic force imaging in superfluid helium and in high magnetic fields. This has been achieved by immobilizing one tine of the tuning fork to stabilize its behavior in superfluid. Images acquired at room temperature and at 50 K are also presented. Frequency–distance curves are shown to be markedly different in superfluid than in air due to a long-range fork–sample interaction in liquid. Evidence is presented that this is due to a change in the hydrodynamic effective mass of the fork as the gap between the fork and sample is reduced. In addition, Q-control has been implemented and used to both increase and decrease the quality factors of tuning forks in both vacuum and superfluid helium. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Phase decomposition of a binary thin film on a patterned substrate

William C. Johnson and S. M. Wise

Appl. Phys. Lett. 81, 919 (2002); http://dx.doi.org/10.1063/1.1497193 (3 pages) | Cited 10 times

Online Publication Date: 22 July 2002

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Two-dimensional simulations of phase decomposition in a binary thin film, which is deposited on a patterned substrate, are performed using the Cahn–Hilliard equation. Phase formation, growth, coarsening, and the resulting two-phase microstructure are strongly influenced by the substrate geometry, film composition, and surface effects. Patterning the substrate can result in the formation of self-organized structures of various sizes and spacings and may provide a method for developing monolayers of periodic nanostructures from an initially homogeneous alloy. © 2002 American Institute of Physics.
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68.55.Nq Composition and phase identification
64.75.-g Phase equilibria
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
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Low-voltage inverted transparent vacuum deposited organic light-emitting diodes using electrical doping

X. Zhou, M. Pfeiffer, J. S. Huang, J. Blochwitz-Nimoth, D. S. Qin, A. Werner, J. Drechsel, B. Maennig, and K. Leo

Appl. Phys. Lett. 81, 922 (2002); http://dx.doi.org/10.1063/1.1496502 (3 pages) | Cited 82 times

Online Publication Date: 22 July 2002

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We demonstrate low-voltage inverted transparent vacuum deposited organic light-emitting diodes employing an indium-tin-oxide coated glass substrate directly as cathode and a semitransparent top Au thin film as anode. The devices comprise an intrinsic 8-tris-hydroxyquinoline aluminum (Alq3) emitting layer sandwiched in between n- and p-doped charge transport layer with appropriate blocking layers. They exhibit low driving voltages (∼4 V for a luminance of ∼100 cd/m2). The devices are about 50% transparent in the Alq3 emission region and emit green light from both sides with a total external current efficiency of about 2.5 cd/A. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices

DNA spintronics

M. Zwolak and M. Di Ventra

Appl. Phys. Lett. 81, 925 (2002); http://dx.doi.org/10.1063/1.1496504 (3 pages) | Cited 47 times

Online Publication Date: 22 July 2002

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We predict, using a tight-binding model, that spin-dependent transport can be observed in short DNA molecules sandwiched between ferromagnetic contacts. In particular, we show that a DNA spin valve can be realized with magnetoresistance values of as much as 26% for Ni and 16% for Fe contacts. Spin-dependent transport can broaden the possible applications of DNA as a component in molecular electronics and shed new light into the transport properties of this important biological molecule. © 2002 American Institute of Physics.
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85.65.+h Molecular electronic devices
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
72.15.Gd Galvanomagnetic and other magnetotransport effects

Electrochromism in Ir–Mg oxide films

A. Azens and C. G. Granqvist

Appl. Phys. Lett. 81, 928 (2002); http://dx.doi.org/10.1063/1.1497189 (2 pages) | Cited 10 times

Online Publication Date: 22 July 2002

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Thin films of IrMgyOz with 2<y<5 were produced by reactive dc magnetron sputtering. Electrochromism was investigated by voltammetric cycling in proprionic acid and by spectrophotometry. The Mg addition yielded enhanced optical modulation and bleached state transparency, while good cycling durability prevailed. © 2002 American Institute of Physics.
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42.79.Wc Optical coatings
78.66.Nk Insulators
78.20.Jq Electro-optical effects
81.15.Cd Deposition by sputtering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Negative differential conductance in the tunnel Schottky contact with two-dimensional channel

Michael N. Feiginov

Appl. Phys. Lett. 81, 930 (2002); http://dx.doi.org/10.1063/1.1497715 (3 pages) | Cited 4 times

Online Publication Date: 22 July 2002

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A semiconductor tunnel structure with negative differential conductance (NDC) is proposed and analyzed theoretically. NDC appears due to tunneling through a Schottky barrier into a quantum well. That can be realized in the structures similar to high electron-mobility transistor (HEMT) with tunneling between the gate and two-dimensional channel. Both diodes (two-terminal devices) and transistors (in particular, HEMTs) with NDC could be realized on the basis of the structures. Such structures could be used for generation of high-frequency radiation. The proposed structure should also have the current–voltage characteristic of N type. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
85.30.Tv Field effect devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.De Semiconductor-device characterization, design, and modeling

Reduction of the light-onset voltage of light-emitting diodes based on a soluble poly(p-phenylene vinylene) by grafting polar molecules onto indium–tin oxide

J. Morgado, A. Charas, and N. Barbagallo

Appl. Phys. Lett. 81, 933 (2002); http://dx.doi.org/10.1063/1.1497440 (3 pages) | Cited 12 times

Online Publication Date: 22 July 2002

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We report on the reduction of the light-onset voltage of light-emitting diodes based on poly[(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] with aluminum cathodes down to 2.2 V by grafting polar molecules onto indium-tin oxide. This value is close to Eg/e = 2.13 V, Eg being the energy gap estimated from the absorption onset and e the electron charge, in spite of the poor electron injection ability of the aluminum cathode. In addition, there is a very efficient suppression of the commonly observed low-voltage current peaks. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
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