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1 Sep 2003

Volume 83, Issue 9, pp. 1689-1898

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 1710 (2003); http://dx.doi.org/10.1063/1.1605792 (3 pages)

G. D. Chern, H. E. Tureci, A. Douglas Stone, R. K. Chang, M. Kneissl, and N. M. Johnson
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Charge storage in undoped hydrogenated amorphous silicon by ambient atomic force microscopy

B. Rezek, T. Mates, J. Stuchlík, J. Kočka, and A. Stemmer

Appl. Phys. Lett. 83, 1764 (2003); http://dx.doi.org/10.1063/1.1606872 (3 pages) | Cited 14 times

Online Publication Date: 26 August 2003

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Hydrogenated amorphous silicon (a-Si:H) layers are prepared by plasma-enhanced chemical vapor deposition on metallized glass substrates. Ambient atomic force microscopy (AFM) is employed for both modification and characterization of a-Si:H films. Voltage pulses of up to 35 V are applied as a cantilever scans the amorphous silicon surface in contact mode AFM. Subsequent detection by Kelvin probe microscopy reveals a persistent negative charge stored in the a-Si:H layers. The stored charge is always negative independent of voltage polarity and results in an upward shift of the Fermi level by as much as 0.1 eV. Only at higher negative voltages (<−15 V) a positively charged oxide layer grows on the surface due to anodic oxidation. A model of the observed phenomena is proposed considering charge transport across a biased contact junction, metastable trapping in band-gap states of a-Si:H, as well as the influence of silicon oxide. © 2003 American Institute of Physics.
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73.61.Cw Elemental semiconductors

Substrate dependent ultrafast dynamics in thin NiFe films

C. A. C. Bosco, A. Azevedo, and L. H. Acioli

Appl. Phys. Lett. 83, 1767 (2003); http://dx.doi.org/10.1063/1.1605246 (3 pages) | Cited 6 times

Online Publication Date: 26 August 2003

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We have studied the ultrafast electronic response of thin NiFe films by femtosecond transient reflectivity measurements. The experiments were performed on films with varying thicknesses, substrates, and pump fluences. It has been observed that for high excitation densities the electron cooling time depends strongly on the nature of the underlying substrate and we attribute our results to transport of hot carriers out of the excited region. In particular, we have observed that for NiFe over NiO, carrier transport should be less important than for NiFe over Si. © 2003 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.66.Bz Metals and metallic alloys
73.61.At Metal and metallic alloys

Piezoelectric, electro-optical, and photoelastic effects in InxGa1−xN/GaN multiple quantum wells

C. H. Chen, W. H. Chen, Y. F. Chen, and T. Y. Lin

Appl. Phys. Lett. 83, 1770 (2003); http://dx.doi.org/10.1063/1.1604176 (3 pages) | Cited 10 times

Online Publication Date: 26 August 2003

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We present microphotoluminescence (PL) and micro-Raman measurements with varying the applied electric field in InxGa1−xN/GaN multiple quantum wells (MQWs). The InGaN A1(LO) phonon was found to show a redshift in frequency with the increase of applied electric field. And, a blueshift in PL spectra has been observed when the applied electric field was increased. Quite interestingly, the change in the refractive index was also observed, which was determined accurately from the interference pattern shown in the emission spectra. This finding correlates very well with the blueshift of PL spectra and the redshift of the InGaN A1(LO) phonon. Based on the stress change induced by the compensation between piezoelectric and external fields, our results firmly establish that strong electro-optical and photoelastic effects do exist in InxGa1−xN/GaN MQWs, which is important in the design of optoelectronic devices. © 2003 American Institute of Physics.
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78.67.De Quantum wells
78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.65.Bn Piezoelectric and electrostrictive constants

Rectifying electrical characteristics of La0.7Sr0.3MnO3/ZnO heterostructure

Ashutosh Tiwari, C. Jin, D. Kumar, and J. Narayan

Appl. Phys. Lett. 83, 1773 (2003); http://dx.doi.org/10.1063/1.1605801 (3 pages) | Cited 43 times

Online Publication Date: 26 August 2003

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We have fabricated a p–n junction, consisting of p-type manganite (La0.7Sr0.3MnO3) and n-type ZnO layers grown on sapphire substrate. This junction exhibits excellent rectifying behavior over the temperature range 20–300 K. Electrical characteristics of La0.7Sr0.3MnO3 (LSMO) film in this heterostructure are found to be strongly modified by the built-in electric field at the junction. It has been shown that by applying the external bias voltage, the thickness of the depletion layer, and hence, the electrical and magnetic characteristics of LSMO film can precisely be modified. © 2003 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification

Effect of hydrogen in dilute InNxSb1−x alloys grown by molecular beam epitaxy

T. D. Veal, I. Mahboob, C. F. McConville, T. M. Burke, and T. Ashley

Appl. Phys. Lett. 83, 1776 (2003); http://dx.doi.org/10.1063/1.1604463 (3 pages) | Cited 12 times

Online Publication Date: 26 August 2003

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The electronic properties and nitrogen bonding configurations are investigated in dilute InNxSb1−x alloys grown by molecular beam epitaxy using a mixed nitrogen and hydrogen plasma. High-resolution electron-energy-loss spectroscopy is used to observe annealing-induced changes in the conduction band electron plasma frequency and plasmon lifetime. X-ray photoelectron spectroscopy of the N 1s core level indicates that a large proportion of the nitrogen in the InNxSb1−x alloy is contained within neutral N–H complexes. Annealing at 300 °C removes hydrogen from these complexes, increasing the concentration of isoelectronic nitrogen acceptors. This increases the ionized impurity scattering and reduces the background conduction electron density. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.30.+q High-frequency effects; plasma effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
61.72.Cc Kinetics of defect formation and annealing

Field emission from carbon black and carbon black/silica nanoparticles dispersed in photoresist

H. Busta, D. Boldridge, R. Myers, E. Edwards, and A. Feinerman

Appl. Phys. Lett. 83, 1779 (2003); http://dx.doi.org/10.1063/1.1606878 (3 pages) | Cited 1 time

Online Publication Date: 26 August 2003

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Carbon black and carbon black mixed with silica nanoparticles were dispersed in Shipley 1818 photoresist and spun onto copper-coated silicon substrates. By using an appropriate amount of carbon black, the films are made conductive, at least in the vertical direction, and exhibit electron emitting properties with macroscopic current densities of about 1 mA/cm2 and turn-on fields ranging from 3 to 5 V/μm. These results are compared to carbon nanotubes (CNTs) also dispersed in photoresist and prepared in a similar manner. The current-extraction field curves exhibit a pronounced peak for the C/SiO2 sample and saturation regions for the C and CNT samples. It is conjectured that resonance tunneling caused by the presence of impurities gives rise to this behavior. The maximum deposition temperature these films experience is 120 °C, which makes them ideal candidates for low-cost, large-area electron and x-ray sources. The role of the photoresist is mainly for providing adhesion of the carbonaceous material to the substrate. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption

Superior Schottky electrode of RuO2 for deep level transient spectroscopy on anatase TiO2

Takahira Miyagi, Masayuki Kamei, Takefumi Mitsuhashi, and Atsushi Yamazaki

Appl. Phys. Lett. 83, 1782 (2003); http://dx.doi.org/10.1063/1.1606869 (3 pages) | Cited 6 times

Online Publication Date: 26 August 2003

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An anatase TiO2 film was epitaxially grown on a conductive Nb-doped single-crystalline SrTiO3 (100) substrate by metalorganic chemical vapor deposition. RuO2 Schottky electrode was fabricated on the epitaxial anatase film by reactive dc magnetron sputtering. The dark I–V and capacitance–voltage characteristics indicated the good rectification and thermal stability of the RuO2/anatase junction. This RuO2/anatase junction enables the stable measurements of deep level transient spectroscopy in the high-temperature region and is a promising Schottky electrode to examine the origins of deep levels in the band gap of anatase. © 2003 American Institute of Physics.
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71.55.Ht Other nonmetals
73.61.Le Other inorganic semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ei Rectification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Cd Deposition by sputtering
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FePt (001) texture development on an Fe–Ta–C magnetic soft underlayer with SiO2/MgO as an intermediate layer

Z. G. Zhang, K. Kang, and T. Suzuki

Appl. Phys. Lett. 83, 1785 (2003); http://dx.doi.org/10.1063/1.1606492 (3 pages) | Cited 30 times

Online Publication Date: 26 August 2003

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In order to develop the FePt (001) texture on an Fe–Ta–C magnetic soft underlayer (SUL), a combined SiO2/MgO intermediate layer is used between the SUL and FePt/MgO laminated recording layer. The function of the amorphous SiO2 layer is to cut the epitaxial growth relationship between the SUL and recording layer and to establish the MgO (200) texture. The thin FePt layers are epitaxially grown on the MgO layers and transformed into (001)-textured L10 FePt films upon annealing. Increasing the surface roughness of the Fe–Ta–C SUL from 0.74 to 2.35 nm does not significantly affect the FePt (001) texture, but has an effect on the FePt grain c-axis dispersion and the FePt L10 phase ordering. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
68.65.Ac Multilayers
75.50.Bb Fe and its alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Ordering oscillation of local composition in melt-processed REBa2Cu3O7−δ superconductors (RE: Sm, Eu, Gd)

A. Hu, M. Murakami, and H. Zhou

Appl. Phys. Lett. 83, 1788 (2003); http://dx.doi.org/10.1063/1.1605262 (3 pages) | Cited 23 times

Online Publication Date: 26 August 2003

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High quality melt-processed GdBa2Cu3O7−δ, (Sm0.5Eu0.5)Ba2Cu3O7−δ and (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ single domains were grown in air and the microstructural origin of their distinguished superconducting performance was investigated by a transmission electron microscope equipped with energy-dispersive spectroscopy. A periodic array of the chemical composition with tens of micrometer correlation was unveiled due to the spatial oscillation of RE (RE: Sm, Eu, and Gd) and Ba around the stoichiometric ratio with a nanometer scale wavelength. For (Sm0.5Eu0.5)Ba2Cu3O7−δ, the temperature dependence of the reversible magnetic moment at certain fields showed two kinks. The first transition followed three-dimensional scaling and yielded dBc2/dT = 1.98 T/K, corresponding to thermal fluctuation of the bulk superconductivity while the second displayed a linear temperature function with slightly lower Tc than bulk Tc and a slope of 0.6 T/K. This may indicate a field-induced pinning scenario with low Tc stripes. © 2003 American Institute of Physics.
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74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
61.66.Bi Elemental solids
61.66.Dk Alloys
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.40.-n Fluctuation phenomena
74.25.Ha Magnetic properties including vortex structures and related phenomena

Electronic structure of cubic Li(Fe0.1Mn1.9)O4 studied with Mössbauer spectroscopy and first-principles calculation

Y. J. Wei, X. G. Xu, C. Z. Wang, C. Li, G. Chen, and F. Wu

Appl. Phys. Lett. 83, 1791 (2003); http://dx.doi.org/10.1063/1.1606494 (3 pages) | Cited 4 times

Online Publication Date: 26 August 2003

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Mössbauer spectrum was collected in Fe3+ doped cubic LiMn2O4 (LiFe0.1Mn1.9O4) by using 57Fe as the radiation source. In the model of the crystal-field theory, the energy gaps between different d orbitals, ΔE(b1g−a1g) and ΔE(b2g−eg), characterize the strength of the Jahn–Teller effect in the crystal. A relationship between the Mössbauer quardrupole splitting and the energy gaps was established, based on which both ΔE(b1g−a1g) and ΔE(b2g−eg) of the [MnO6] octahedron in LiFe0.1Mn1.9O4 are estimated to be about 0.41 and 0.30 eV, respectively. Electronic structure of LiMn2O4 was studied theoretically via ab initio calculation based on the density-functional theory. Calculation shows that a gap about 0.28 eV between the filled Mn d bands is equivalent to ΔE(b2g−eg). It also shows that the first unoccupied states are dominated by Mn 3d contribution essentially from both a1g and b1g of Mn d states. Distance between the two peaks in the first unoccupied band was used to calculate ΔE(b1g−a1g), which is about 0.36 eV. The Mössbauer quardrupole splitting characterizes Jahn–Teller distortion and its effect on the fine structure of Mn 3d bands. © 2003 American Institute of Physics.
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71.20.Ps Other inorganic compounds
76.80.+y Mössbauer effect; other γ-ray spectroscopy
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.70.Ch Crystal and ligand fields
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.70.Jp Nuclear states and interactions

Thermal transport in stacked superconductor–normal metal–superconductor Josephson junctions

Yonuk Chong, P. D. Dresselhaus, and S. P. Benz

Appl. Phys. Lett. 83, 1794 (2003); http://dx.doi.org/10.1063/1.1606491 (3 pages) | Cited 14 times

Online Publication Date: 26 August 2003

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Nb/MoSi2/Nb stacked superconductor–normal metal–superconductor (SNS) Josephson junctions has proven to be a good candidate for high-density series arrays for Josephson voltage-standard applications. As the junction density increases, self-heating becomes an issue because the high power density per junction (1 W/cm2) generates significant power dissipation under typical operating conditions. In this letter, we analyze the heating effect of these sandwich-type SNS junctions using a model to quantitatively estimate and predict thermal-transport properties of the stacked structures. We describe several strategies that reduce heating and demonstrate improved properties of stacked-junction arrays with enhanced cooling capacity.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
85.25.Cp Josephson devices
74.25.F- Transport properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

X-ray photoemission electron microscopy investigation of magnetic thin film antidot arrays

L. J. Heyderman, F. Nolting, and C. Quitmann

Appl. Phys. Lett. 83, 1797 (2003); http://dx.doi.org/10.1063/1.1605804 (3 pages) | Cited 17 times

Online Publication Date: 26 August 2003

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Periodic square arrays of antidots in 10 nm-thick cobalt films have been investigated with antidot periods, p, ranging from 2 μm down to 200 nm and various ratios of antidot size to antidot separation, w/d. For p = 2 μm, the extent of modification of the thin film magnetic domain structure increases with increasing w/d, forming domains pinned diagonally between antidots for w/d ≥ 0.2 and resulting in a two-dimensional periodic checked domain contrast commensurate with the antidot lattice for w/d ≥ 0.9. As p is decreased while maintaining d ≈ w, we observe a dramatic change in the magnetic domain configuration at p = 400 nm resulting in chains of magnetic domains running parallel to the intrinsic hard axis and with lengths corresponding to a multiple of the antidot period. © 2003 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.75.-c Magnetic properties of nanostructures
68.37.Xy Scanning Auger microscopy, photoelectron microscopy

Pinned synthetic ferrimagnets with perpendicular anisotropy and tuneable exchange bias

J. Sort, B. Rodmacq, S. Auffret, and B. Dieny

Appl. Phys. Lett. 83, 1800 (2003); http://dx.doi.org/10.1063/1.1606495 (3 pages) | Cited 22 times

Online Publication Date: 26 August 2003

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Pinned synthetic ferrimagnets (syFerri) with perpendicular-to-plane magnetic anisotropy, of the form AP1/Ru/AP2/FeMn [where AP1 and AP2 are (Co/Pt) multilayers], have been prepared and characterized. The magnitudes of the exchange bias fields of both AP1 and AP2 can be tuned at room temperature by simply varying the relative number of (Co/Pt) repeats in each multilayer. This effect can be quantitatively interpreted by considering the different energy contributions involved during magnetization reversal. Moreover, from the values of these fields, the characteristic parameters of the system (i.e., coupling strength through the Ru and AP2/FeMn pinning energy), can be evaluated. Interestingly, an extended plateau with a virtually constant magnetization is observed around zero field when the number of Co/Pt repeats in AP1 is equal or larger than in AP2. This is very appealing for field sensor or memories applications using spin valves or tunnel junctions with perpendicular anisotropy, since it offers a large dynamic range over which the magnetic configuration of the syFerri remains stable. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Preparation of MgB2 tapes using a nanocrystalline partially reacted precursor

C. Fischer, C. Rodig, W. Häßler, O. Perner, J. Eckert, K. Nenkov, G. Fuchs, H. Wendrock, B. Holzapfel, and L. Schultz

Appl. Phys. Lett. 83, 1803 (2003); http://dx.doi.org/10.1063/1.1606498 (3 pages) | Cited 39 times

Online Publication Date: 26 August 2003

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Fe-cladded MgB2 conductors have been prepared by the powder-in-tube method using mechanically alloyed nanocrystalline Mg+2B powder mixtures consisting of the constituents Mg, B, and MgB2 as precursor. Despite low Tc values of about 31 K, maximum critical current densities (Jc) of 22 and 7 kA/cm2 in external magnetic fields of 7.5 and 10 T, respectively, are achieved at 4.2 K. These excellent values can mainly be attributed to the very fine-grained microstructure of the superconducting phase. Higher values have only been reported for tapes doped with SiC nanoparticles. The irreversibility fields Hirr of these tapes are 9.5 and 4.2 T at 10 and 20 K, respectively. © 2003 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.62.Dh Effects of crystal defects, doping and substitution
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
74.25.Sv Critical currents
74.25.Op Mixed states, critical fields, and surface sheaths
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Antiferromagnetic interlayer exchange coupling across epitaxial, Ge-containing spacers

R. R. Gareev, D. E. Bürgler, R. Schreiber, H. Braak, M. Buchmeier, and P. A. Grünberg

Appl. Phys. Lett. 83, 1806 (2003); http://dx.doi.org/10.1063/1.1606102 (3 pages) | Cited 3 times

Online Publication Date: 26 August 2003

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We give experimental evidence of antiferromagnetic interlayer exchange coupling of Fe(001) layers across epitaxial, Ge-containing spacers consisting of either Ge wedges embedded between two Si boundary layers or Si–Ge-multilayers. The coupling strengths are of the order of 1 mJ/m2 and decay on a length scale below 2 Å as determined from magneto-optic Kerr effect and Brillouin light scattering. The coupling evolves with the spacer thickness from ferromagnetic to prevailing 90° or antiferromagnetic for Ge wedges and Si–Ge multilayers, respectively. The bilinear coupling is comparable in both cases, but the biquadratic contribution is suppressed for Si–Ge-multilayer spacers. Thus, Si–Ge-multilayer spacers give rise to perfect antiparallel alignment of the Fe film magnetizations. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Observation of MnP magnetic clusters in room-temperature ferromagnetic semiconductor Zn1−xMnxGeP2 using nuclear magnetic resonance

Taesoon Hwang, Jeong Hyun Shim, and Soonchil Lee

Appl. Phys. Lett. 83, 1809 (2003); http://dx.doi.org/10.1063/1.1605260 (3 pages) | Cited 9 times

Online Publication Date: 26 August 2003

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We investigated chalcopyrite Zn1−xMnxGeP2 polycrystals, which have been reported as a room-temperature ferromagnetic semiconductor, with Mn concentrations of x = 0.08 and 0.15 using 55Mn and 31P nuclear magnetic resonance spectroscopy. The samples were made by the same process and showed the same crystallographic and magnetic behavior as in the previous report, but the experimental results indicated that more than 90% of Mn atoms were in a MnP impurity phase and the MnP cluster size was tens of nanometers. No evidence of Mn atom substitution in the host ZnGeP2 lattice was observed and the magnetic property of Zn1−xMnxGeP2 was determined to be that of the MnP magnetic clusters, at least in the bulk. The inconsistency of the conclusions with x-ray diffraction data is a result of the weak crystallinity of MnP phase. © 2003 American Institute of Physics.
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76.60.-k Nuclear magnetic resonance and relaxation
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
61.66.Fn Inorganic compounds

Spin polarization and magnetotransport of Mn–Sb alloys in magnetic tunnel junctions

Alex F. Panchula, Christian Kaiser, Andrew Kellock, and Stuart S. P. Parkin

Appl. Phys. Lett. 83, 1812 (2003); http://dx.doi.org/10.1063/1.1606108 (3 pages) | Cited 5 times

Online Publication Date: 26 August 2003

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The spin polarization of MnxSb1−x for x = 0.35–0.45 has been explored via magnetic tunnel junctions using CoFe counterelectrodes and via superconducting tunneling spectroscopy using Al counterelectrodes. MnxSb1−x with x ∼ 0.45 shows a tunneling spin polarization of ∼30% at 0.25 K, and a tunneling magnetoresistance of ∼18% at 10 K both of which are very similar to previously reported data on NiMnSb alloys. These results support the notion that surface segregation of Mn and Sb reduces the spin polarization of the purported half-metal NiMnSb. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
85.75.Mm Spin polarized resonant tunnel junctions
75.47.Np Metals and alloys
68.35.Dv Composition, segregation; defects and impurities
74.50.+r Tunneling phenomena; Josephson effects
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Voltage-variable microwave delay line using ferroelectric liquid crystal with aligned submicron polymer fibers

Hideo Fujikake, Takao Kuki, Hirokazu Kamoda, Fumio Sato, and Toshihiro Nomoto

Appl. Phys. Lett. 83, 1815 (2003); http://dx.doi.org/10.1063/1.1605795 (3 pages) | Cited 8 times

Online Publication Date: 26 August 2003

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This letter describes a variable microwave delay line that uses a thick ferroelectric liquid crystal film stabilized by aligned polymer fibers of submicron diameter. The delay line consists of a microstrip transmission line with a 50-μm-thick liquid crystal film as the dielectric material. The conical axis of the helical alignment of the ferroelectric liquid crystal molecules can be anchored in the microwave propagation direction by aligned polymer fibers dispersed in the liquid crystal film without conventional alignment layers coated on substrates. The phase shift of microwaves passed through the device could be varied by applying a voltage across the film to loosen the liquid crystal helical alignment. © 2003 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
42.79.Kr Display devices, liquid-crystal devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals

Properties of lanthanum-doped Bi4Ti3O12–SrBi4Ti4O15 intergrowth ferroelectrics

Jun Zhu, Xiao-Bing Chen, Wang-Ping Lu, Xiang-Yu Mao, and Rong Hui

Appl. Phys. Lett. 83, 1818 (2003); http://dx.doi.org/10.1063/1.1606496 (3 pages) | Cited 16 times

Online Publication Date: 26 August 2003

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Lanthanum-doped intergrowth ferroelectrics, (Bi,La)4Ti3O12–Sr(Bi,La)4Ti4O15 [BLT–SBLT(x)], have been prepared. It is found that the remnant polarization (2Pr) of Bi4Ti3O12–SrBi4Ti4O15 (BIT–SBTi) is enlarged. The 2Pr of BLT–SBLT(0.50) has a maximum value of 25.6 μC/cm2. Assuming that the Curie temperature of BLT–SBLT(x) is the average value of the two constituents, La content in both BLT and SBLT can be estimated on the basis of the fact that the crystal structure of BLT–SBLT(x) is not affected by doping. The result shows that when x is not larger than 1.25, La content in BIT is higher than that in SBTi, but when x is 1.50, La content in SBTi is higher. It coincides with the variation of d(118) and the relaxation characteristics of BLT–SBLT(1.50). © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.B- Phase transitions and Curie point
77.22.Gm Dielectric loss and relaxation
77.80.Dj Domain structure; hysteresis

Electrostrictive and dielectric properties of stretched poly(vinylidene fluoride–trifluoroethylene) copolymers at cryogenic temperatures

Chen Ang, Zhi Yu, and L. E. Cross

Appl. Phys. Lett. 83, 1821 (2003); http://dx.doi.org/10.1063/1.1606101 (3 pages) | Cited 3 times

Online Publication Date: 26 August 2003

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The electrostrictive property and dielectric behavior of the stretched poly (vinylidene fluoride–trifluoroethylene) copolymers, denoted as P(VDF–TrFE), have been studied at cryogenic temperatures. Polarization hysteresis loops and high electrostrictive performance (strain ∼1%) are obtained at room temperature. An obvious dielectric relaxation process is observed and the relaxation rate follows the Vogel–Fulcher relation with TVF = 160 K, U = 0.18 eV, ν0 = 5.7×1012 Hz. The dielectric relaxation behavior and high strain level decrease quickly with decreasing temperature, and below 160 K only a small strain level (∼0.1%) and an “intrinsic” dielectric constant sustains. The correlation of dielectric behavior and strain activity and the physical mechanism of the quick suppression of the strain with decreasing temperature are briefly discussed. The results indicate that a high dielectric constant is critical for obtaining high electrostrictive strains in the polymers at a reasonable electric field. © 2003 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.65.Bn Piezoelectric and electrostrictive constants
77.80.Dj Domain structure; hysteresis
77.22.Gm Dielectric loss and relaxation
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)

Influence of ultraviolet illumination on the poling characteristics of lithium niobate crystals

Manfred Müller, Elisabeth Soergel, and Karsten Buse

Appl. Phys. Lett. 83, 1824 (2003); http://dx.doi.org/10.1063/1.1606504 (3 pages) | Cited 28 times

Online Publication Date: 26 August 2003

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The poling characteristics of lithium niobate crystals under ultraviolet laser illumination are investigated. Light with a wavelength around 334 nm permanently decreases the coercive field of the crystal and is used to demonstrate optical control of domain patterning. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.82.Ms Insulators
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Mesoscopic ferroelectric cell arrays prepared by imprint lithography

Catalin Harnagea, Marin Alexe, Jörg Schilling, Jinsub Choi, Ralf B. Wehrspohn, Dietrich Hesse, and Ulrich Gösele

Appl. Phys. Lett. 83, 1827 (2003); http://dx.doi.org/10.1063/1.1606870 (3 pages) | Cited 35 times

Online Publication Date: 26 August 2003

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Arrays of mesoscopic ferroelectric (Pb,Zr)TiO3 cells with lateral sizes from several micrometers down to below 300 nm were prepared applying nanoimprint lithography. The ferroelectric properties of the mesoscopic cells were investigated by scanning force microscopy in piezoresponse mode. The best chemical route to obtain ferroelectric cells was found to be the sol-gel method. Using Nb-doped SrTiO3 single crystals as bottom electrodes, the crystallization into the ferroelectric phase was uniform with grain sizes in the 35 nm range. © 2003 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
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)
85.35.-p Nanoelectronic devices
85.50.Gk Non-volatile ferroelectric memories
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.37.Ps Atomic force microscopy (AFM)

Al2O3 prepared by atomic layer deposition as gate dielectric on 6H-SiC(0001)

K. Y. Gao, Th. Seyller, L. Ley, F. Ciobanu, G. Pensl, A. Tadich, J. D. Riley, and R. G. C. Leckey

Appl. Phys. Lett. 83, 1830 (2003); http://dx.doi.org/10.1063/1.1609053 (3 pages) | Cited 38 times

Online Publication Date: 26 August 2003

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Al2O3 films were deposited as alternative gate dielectric on hydrogen-terminated 6H-SiC(0001) by atomic layer chemical vapor deposition and characterized by photoelectron spectroscopy (PES) and admittance measurements. The PES results indicate an abrupt interface free of significant Si–suboxide contributions where the Al2O3 layer is connected to SiC by bridging oxygen atoms. The admittance measurements yield an interface state density which is lower than that of the thermally formed oxide and show in particular no increase toward the conduction band edge. Furthermore, a nearly symmetrical band alignment of Al2O3 on 6H-SiC with offsets of 2.2 and 1.8 eV is determined for the valence and conduction bands, respectively. This makes Al2O3 a serious competitor to thermal oxides as gate insulator in SiC devices. © 2003 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states

E-field-induced polarization rotation in Pb(Mg1/3Nb2/3)1−xTixO3 crystal

Chi-Shun Tu, I.-C. Shih, V. Hugo Schmidt, and R. Chien

Appl. Phys. Lett. 83, 1833 (2003); http://dx.doi.org/10.1063/1.1602558 (3 pages) | Cited 28 times

Online Publication Date: 26 August 2003

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A sequence of field-induced phase transformations was observed by means of a polarizing microscope on a (111)-cut single crystal Pb(Mg1/3Nb2/3)0.67Ti0.33O3 at room temperature with an electric field applied along the [111] direction. As electric field increases, polarizations of the rhombohedral R domains whose polar directions are not along [111] rotate first toward a tetragonal T phase associated with 90° domain walls. Then the crystal gradually reaches total optical extinction for all polarizer angles at 12 kV/cm, indicating a single [111] rhombohedral R111 domain with polarization aligned with the electric field. These field-induced phase transformations are irreversible and proceed most likely through MA-type monoclinic distortions, i.e., R→MA→T→MA→R111. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
64.70.K- Solid-solid transitions
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Self-assembled NiSi quantum-dot arrays on epitaxial Si0.7Ge0.3 on (001)Si

W. W. Wu, J. H. He, S. L. Cheng, S. W. Lee, and L. J. Chen

Appl. Phys. Lett. 83, 1836 (2003); http://dx.doi.org/10.1063/1.1605242 (3 pages) | Cited 6 times

Online Publication Date: 26 August 2003

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Self-assembled NiSi quantum-dot arrays have been grown on relaxed epitaxial Si0.7Ge0.3 on(001)Si. The formation of the one-dimensional ordered structure is attributed to the nucleation of NiSi nanodots on the surface undulations induced by step bunching on the surface of SiGe film owing to the miscut of the wafers from normal to the (001)Si direction. The two-dimensional pseudohexagonal structure was achieved under the influence of repulsive stress between nanodots. Since the periodicity of surface bunching can be tuned with appropriate vicinality and misfit, the undulated templates promise to facilitate the growth of ordered silicide quantum dots with selected periodicity and size. © 2003 American Institute of Physics.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.16.Dn Self-assembly
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