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Top 20 Most Read Articles
September 2006
The 20 articles with the most full-text downloads during the month, in descending order.
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Ferroelectric thin films: Review of materials, properties, and applications J. Appl. Phys. 100, 051606 (2006); http://dx.doi.org/10.1063/1.2336999 (46 pages) Online Publication Date: 12 September 2006
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An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems’ applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems’ applications, and permittivity and loss in ferroelectric films—important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures.
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Constructal theory of generation of configuration in nature and engineering J. Appl. Phys. 100, 041301 (2006); http://dx.doi.org/10.1063/1.2221896 (27 pages) Online Publication Date: 29 August 2006
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Constructal theory is the view that the generation of flow configuration is a physics phenomenon that can be based on a physics principle (the constructal law): “For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it” [A. Bejan,
Advanced Engineering Thermodynamics, 2nd ed. (Wiley, New York, 1997);
Int. J. Heat Mass Transfer, 40, 799 (1997)
]. This principle predicts natural configuration across the board: river basins, turbulence, animal design (allometry, vascularization, locomotion), cracks in solids, dendritic solidification, Earth climate, droplet impact configuration, etc. The same principle yields new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information. This review describes a paradigm that is universally applicable in natural sciences, engineering and social sciences.
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A comprehensive review of ZnO materials and devices J. Appl. Phys. 98, 041301 (2005); http://dx.doi.org/10.1063/1.1992666 (103 pages) Online Publication Date: 30 August 2005
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The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60 meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by
Bunn [Proc. Phys. Soc. London 47, 836 (1935)
], studies of its vibrational properties with Raman scattering in 1966 by
Damen et al. [Phys. Rev. 142, 570 (1966)
], detailed optical studies in 1954 by
Mollwo [Z. Angew. Phys. 6, 257 (1954)
], and its growth by chemical-vapor transport in 1970 by
Galli and Coker [Appl. Phys. Lett. 16, 439 (1970)
]. In terms of devices, Au Schottky barriers in 1965 by
Mead [Phys. Lett. 18, 218 (1965)
], demonstration of light-emitting diodes (1967) by
Drapak [Semiconductors 2, 624 (1968)
], in which Cu2O was used as the p-type material, metal-insulator-semiconductor structures (1974) by
Minami et al. [Jpn. J. Appl. Phys. 13, 1475 (1974)
], ZnO/ZnSe n-p junctions (1975) by
Tsurkan et al. [Semiconductors 6, 1183 (1975)
], and Al/Au Ohmic contacts by
Brillson [J. Vac. Sci. Technol. 15, 1378 (1978)
] were attained. The main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO, as recently discussed by
Look and Claflin [Phys. Status Solidi B 241, 624 (2004)
]. While ZnO already has many industrial applications owing to its piezoelectric properties and band gap in the near ultraviolet, its applications to optoelectronic devices has not yet materialized due chiefly to the lack of p-type epitaxial layers. Very high quality what used to be called whiskers and platelets, the nomenclature for which gave way to nanostructures of late, have been prepared early on and used to deduce much of the principal properties of this material, particularly in terms of optical processes. The suggestion of attainment of p-type conductivity in the last few years has rekindled the long-time, albeit dormant, fervor of exploiting this material for optoelectronic applications. The attraction can simply be attributed to the large exciton binding energy of 60 meV of ZnO potentially paving the way for efficient room-temperature exciton-based emitters, and sharp transitions facilitating very low threshold semiconductor lasers. The field is also fueled by theoretical predictions and perhaps experimental confirmation of ferromagnetism at room temperature for potential spintronics applications. This review gives an in-depth discussion of the mechanical, chemical, electrical, and optical properties of ZnO in addition to the technological issues such as growth, defects, p-type doping, band-gap engineering, devices, and nanostructures.
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Preface: Science of ferroelectric thin films and application to devices J. Appl. Phys. 100, 051501 (2006); http://dx.doi.org/10.1063/1.2336995 (1 page) Online Publication Date: 12 September 2006
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High-κ gate dielectrics: Current status and materials properties considerations J. Appl. Phys. 89, 5243 (2001); http://dx.doi.org/10.1063/1.1361065 (33 pages)
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Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward successful integration into the expected processing conditions for future CMOS technologies, especially due to their tendency to form at interfaces with Si (e.g. silicates). These pseudobinary systems also thereby enable the use of other high-κ materials by serving as an interfacial high-κ layer. While work is ongoing, much research is still required, as it is clear that any material which is to replace SiO2 as the gate dielectric faces a formidable challenge. The requirements for process integration compatibility are remarkably demanding, and any serious candidates will emerge only through continued, intensive investigation. © 2001 American Institute of Physics. |
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Growth modes of carbon nanotubes on metal substrates J. Appl. Phys. 100, 044309 (2006); http://dx.doi.org/10.1063/1.2219000 (10 pages) Online Publication Date: 23 August 2006
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Growth temperature induced changes in Al/Fe thin film catalysts are examined for chemical vapor deposition of carbon nanotubes directly on metal substrates. The film thickness, growth temperature, and supporting substrate affect the size and the density of Fe catalyst nanoparticles which in turn control the diameter, length, and single versus multiwalled nature of carbon nanotubes. Growths on two metal substrates, Au and Mo, using sputter deposited Al/Fe thin films are compared by transmission and scanning electron microscopy, and Raman analyses. Striking differences in the growth modes are observed with Au substrate enhancing multiwalled nanotube growth with metal catalyst particles at the tip away from the substrate and Mo substrate promoting single-walled nanotube growth with the catalyst nanoparticles remaining on the substrate. Oxidative treatment of Mo underlayer (i.e., relatively thick layer Mo sputtered on Au prior to Al/Fe catalyst deposition) can also induce nanotube growth with catalyst particles at the tips but with single-walled structure. These results suggest the importance of the support catalyst (Al/AlxOy) adhesion strength on substrates in determining nanotube growth modes.
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Vapor-liquid-solid mechanisms: Challenges for nanosized quantum cluster/dot/wire materials J. Appl. Phys. 100, 044315 (2006); http://dx.doi.org/10.1063/1.2236163 (12 pages) Online Publication Date: 25 August 2006
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The growth mechanism model of a nanoscaled material is a critical step that has to be refined for a better understanding of a nanostructure’s dot/wire fabrication. To do so, the growth mechanism will be discussed in this paper and the influence of the size of the metallic nanocluster starting point, referred to later as “size effect,” will be studied. Among many of the so-called size effects, a tremendous decrease of the melting point of the metallic nanocluster changes the physical properties as well as the physical/mechanical interactions inside the growing structure composed of a metallic dot on top of a column. The thermodynamic size effect is related to the bending or curvature of chains of atoms, giving rise to the weakening of bonds between them; this size or curvature effect is described and approached to crystal nanodot/wire growth. We will describe this effect as that of a “cooking machine” when the number of atoms decreases from ∼ 1023 at./cm3 for a bulk material to a few tens of them in a 1–2 nm diameter sphere. The decrease of the number of atoms in a metallic cluster from such an enormous quantity is accompanied by a lowering of the melting temperature that extends from 200 up to 1000 K, depending on the metallic material and its size under study. In this respect, the vapor-liquid-solid (VLS) model, which is the most utilized growth mechanism for quantum nanowires and nanodots, is critically exposed to size or curvature effects (CEs). More precisely, interactions in the vicinity of the growth regions should be reexamined. Some results illustrating the growth of micrometer-/nanometer-sized materials are presented in order to corroborate the CE/VLS models utilized by many research groups in today’s nanosciences world. Examples of metallic clusters and semiconducting wires will be presented. The results and comments presented in this paper can be seen as a challenge to be overcome. From them, we expect that in a near future an improved model can be exposed to the scientific community.
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Polymer memory device based on conjugated polymer and gold nanoparticles J. Appl. Phys. 100, 054309 (2006); http://dx.doi.org/10.1063/1.2337252 (5 pages) Online Publication Date: 8 September 2006
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Electrical bistability is demonstrated in a polymer memory device with an active layer consisting of conjugated poly(3-hexylthiophene) and gold nanoparticles capped with 1-dodecanethiol sandwiched between two metal electrodes. The device was fabricated through a simple solution processing technique and exhibited a remarkable electrical bistable behavior. Above a threshold voltage the pristine device, which was in a low conductivity state, exhibited an increase in conductivity by more than three orders of magnitude. The device could be returned to the low conductivity state by applying a voltage in the reverse direction. The electronic transition is attributed to an electric-field-induced charge transfer between the two components in the system. The conduction mechanism changed from a charge-injection-controlled current in the low conductivity state to a charge-transport-controlled current in the high conductivity state. In the high conductivity state the conduction was dominated by a field-enhanced thermal excitation of trapped charges at room temperature, while it is dominated by charge tunneling at low temperatures. The device exhibited excellent stability in both the conductivity states and could be cycled between the two states for numerous times. The device exhibits tremendous potential for its application as fast, stable, low-cost, high storage density nonvolatile electronic memory.
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UV∕ozone treated Au for air-stable, low hole injection barrier electrodes in organic electronics J. Appl. Phys. 100, 053701 (2006); http://dx.doi.org/10.1063/1.2336345 (6 pages) Online Publication Date: 1 September 2006
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Ultraviolet and x-ray photoelectron spectroscopies were used to study electronic properties of interfaces between Au substrates and a number of organic semiconductors (small molecules and polymers). Au surface work function (ϕ) values before organic deposition were ∼ 4.7 eV (exposed to air), ∼ 5.2 eV (atomically clean), and ∼ 5.5 eV (UV∕ozone treated). The high ϕ obtained for UV/O3 treated Au was due to Au oxide formation and surface-adsorbed carbon and oxygen species. Au surface morphology remained essentially unchanged by UV∕ozone exposure, as observed by atomic force microscopy. Hole injection barriers (HIBs) at interfaces between UV∕ozone treated Au and the organic semiconductors were systematically lower than those for untreated Au (both atomically clean and air exposed). Reductions in HIB of up to 1.4 eV (for p-sexiphenyl) were achieved. In addition, good long-term stability of reduced HIBs of such interfaces was observed for air storage of up to several days.
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Band parameters for III–V compound semiconductors and their alloys J. Appl. Phys. 89, 5815 (2001); http://dx.doi.org/10.1063/1.1368156 (61 pages)
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We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other. © 2001 American Institute of Physics. |
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Evidence for electrical spin tunnel injection into silicon J. Appl. Phys. 100, 043717 (2006); http://dx.doi.org/10.1063/1.2229870 (4 pages) Online Publication Date: 30 August 2006
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Electrical spin injection into silicon was studied in a ferromagnet∕insulator∕silicon∕insulator∕ferromagnet structure, where the insulator is Si3N4. Si3N4 barriers conduct by hopping conduction at low voltages, but switch to Fowler-Nordheim tunneling at high voltages. In the Fowler-Nordheim tunneling regime a magnetic field dependence of the output current consistent with spin dependent transport through the silicon is observed; in the hopping conduction regime reduced magnetic field dependence of the output current is observed. This voltage dependence of the magnetic sensitivity strongly supports the existence of spin injection into silicon. After correction for Lorentz magnetoresistance, the magnitude of this signal is 4.1%±0.5% (12%±5%) for p-type (n-type) Si.
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J. Appl. Phys. 100, 044321 (2006); http://dx.doi.org/10.1063/1.2335396 (8 pages) Online Publication Date: 30 August 2006
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A series of Fe catalysts, with different mean diameters, supported on alumina with different molar ratios, was studied before and after carbon single walled nanotubes growth using magnetic measurements and Raman scattering techniques (laser excitation wavelengths from 1.17 to 2.54 eV) to follow changes on catalyst particle size and composition, as well as the relationship between particle size and diameter of nanotubes grown. In all cases, an increase and redistribution of the particle size after the growth was concluded based on the blocking temperature values and Langevin function analysis. This is explained in terms of agglomeration of particles due to carbon-induced liquefaction accompanied with an increase in the catalyst mobility. For large particles no direct correlation between the catalyst size and the nanotube diameters was observed.
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High-K dielectrics for the gate stack J. Appl. Phys. 100, 051610 (2006); http://dx.doi.org/10.1063/1.2336996 (14 pages) Online Publication Date: 15 September 2006
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This article gives an overview of recent developments in the search for the next-generation dielectric for the complementary metal-oxide semiconductor gate stack. After introducing the main quantities of interest, the paper concentrates on a figure of merit that connects two main properties of the gate stack, namely, the leakage current and the capacitance. This is done for single layers as well as for bilayers consisting of interfacial SiOx and a high-K dielectric. In the case of the bilayers, the impact of the interfacial layer SiOx is enormous, reducing the leakage current by an order of magnitude per monolayer. This extreme dependance makes a good correlation between the leakage and the structural parameters nearly impossible. This is illustrated using numerical examples designed to help the reader evaluate the orders of magnitude involved. The origin of the interfacial layer is traced back by means of thermodynamic considerations. As the estimates put forward in the literature do not correspond to the results observed, a detailed review is made, and additional mechanisms are suggested. By using reasonable values for the Gibbs free energy of an interfacial solid silicon oxide phase it is demonstrated how the reaction equilibria shift. Such an interface phase may fundamentally change the stability criteria of oxides on Si. Furthermore, it can also provide a major source of electronic defects that will affect the device performance. Finally, a second figure of merit is introduced that connects the capacitance with a strongly reduced carrier mobility, which might also be related to the same electronic defects.
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Nitrogen-doped p-type ZnO films prepared from nitrogen gas radio-frequency magnetron sputtering J. Appl. Phys. 100, 053705 (2006); http://dx.doi.org/10.1063/1.2337766 (4 pages) Online Publication Date: 12 September 2006
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Wide band gap nitrogen-doped p-type ZnO films are prepared by radio-frequency magnetron sputtering from a 99.99% purity ZnO target. The sputtering gas is Ar mixed with various flow rates of nitrogen gas. Hole concentrations increase from 1.89×1015 to 2.11×1019 cm−3 as the N2 flow rate decreases from 15 to 6 SCCM (SCCM denotes cubic centimeter per minute at STP), i.e., increasing N2 flow rate above 6 SCCM decreases the p-type carrier concentration. Microphotoluminescence (PL) spectra peaks are in the near-UV range and change from 384 nm (3.23 eV) to 374 nm (3.32 eV) with increasing N2 flow rate. The PL peaks agree with the band gap of bulk ZnO, which comes from the recombination of free excitons. Raman spectra show six peaks: 436 (E2 high-frequency phonon mode for undoped ZnO film), 581 [A1 (LO) mode in ZnO:N film], 275, 508, 640, and 854 cm−1 (local vibrational modes of Raman features in N-doped ZnO film).
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Theory for equilibrium 180° stripe domains in PbTiO3 films J. Appl. Phys. 100, 051601 (2006); http://dx.doi.org/10.1063/1.2337360 (17 pages) Online Publication Date: 7 September 2006
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A thermodynamic theory is developed for equilibrium 180° stripe domains in ferroelectric thin films on insulating substrates. Such stripe domains form to minimize the energy of the depolarizing field, and lead to a suppression of TC in thin films. Expressions including depolarizing field and domain wall energy are developed and applied to coherently strained PbTiO3 films on SrTiO3 substrates, with an upper boundary condition of either a dielectric (SrTiO3), a conductor, or vacuum. An elastic solution appropriate for epitaxially strained stripe domains and 180° domain walls is presented. We minimize the full nonlinear free energy using a numerical technique to obtain equilibrium polarization and field distributions, and determine the equilibrium stripe period as a function of temperature and film thickness for each upper boundary condition. While the stripe periods found agree reasonably well with the existing analytical solution using a linearized free energy, the suppression of TC as film thickness decreases is as much as a factor of 10 smaller than that given by the linear solution.
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Organic light-emitting devices using polyacene derivatives as a hole-transporting layer J. Appl. Phys. 100, 044507 (2006); http://dx.doi.org/10.1063/1.2266173 (5 pages) Online Publication Date: 23 August 2006
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Three polyacene derivatives, 2-tert-butyl-9,10-di(2-naphthyl)anthracene (TBADN), 9,9′,10,10′- tetraphenyl-2,2′-bianthracene, and 5,6,11,12-tetraphenylnaphthacene (rubrene), are found to successfully function as hole-transporting layers (HTLs) in red organic light-emitting devices (OLEDs) using tetraphenyldibenzoperiflanthene as an emitter. Compared with an OLED with the most widely used HTL material, the arylamine derivative, 4,4′-bis(N-phenyl-1-naphthylamino)biphenyl (NPB), the OLEDs with the polyacene derivatives exhibit advantageous performance such as lower driving voltage, higher electroluminescence efficiency, or longer luminance lifetime, depending on the employed HTL material. Current efficiency of the red OLED with a TBADN HTL is 5.5 cd/A with Commission Internationale de L’Eclairage chromaticity coordinates of (x = 0.66, y = 0.34), which is much higher than the value of 2.1 cd/A with the same chromaticity for the OLED with a NPB HTL. The driving voltage and luminance lifetime of the red OLED with rubrene HTL are improved compared with the OLED with a NPB HTL. The hole injection properties of the proposed HTL materials are discussed. The results indicate that the polyacene derivatives are promising for use in OLEDs as a class of HTLs, expanding the variety of HTL materials available for optimizing the performance of OLEDs.
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GaAs, AlAs, and AlxGa1−xAs J. Appl. Phys. 58, R1 (1985); http://dx.doi.org/10.1063/1.336070 (29 pages)
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The AlxGa1−xAs/GaAs heterostructure system is potentially useful material for high‐speed digital, high‐frequency microwave, and electro‐optic device applications. Even though the basic AlxGa1−xAs/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters. Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J. S. Blakemore, J. Appl. Phys. 53, R123 (1982)]. The purpose of this review is (i) to obtain and clarify all the various material parameters of AlxGa1−xAs alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications. A complete set of material parameters are considered in this review for GaAs, AlAs, and AlxGa1−xAs alloys. The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs). The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic‐band structure, (7) external perturbation effects on the band‐gap energy, (8) effective mass, (9) deformation potential, (10) static and high‐frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Fröhlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties. Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x. Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well. Other parameters, e.g., electronic‐band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction. However, some kinds of the material parameters, e.g., lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder. It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data. A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid‐state physics. Key properties of the material parameters for use in research work and a variety of AlxGa1−xAs/GaAs device applications are also discussed in detail. |
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Surface plasmon resonance in conducting metal oxides J. Appl. Phys. 100, 054905 (2006); http://dx.doi.org/10.1063/1.2222070 (4 pages) Online Publication Date: 8 September 2006
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We report the initial observation of surface plasmon resonance (SPR) in a conducting metal oxide thin film. The SPR phenomenon has been observed by attenuated total reflection of near-infrared radiation and is in agreement with electron energy loss spectroscopy measurements. To date, only metals are known to exhibit surface plasmon resonance and only noble metals have practical application. According to theory SPR should be observable in any conductor. This theoretical prediction is verified in the present study. The compositions of many conducting metal oxides are systematically variable, suggesting a significant advance in thin film characterization and innovative possibilities for versatile and sensitive chemical sensing applications.
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Influence of annealing on the structural and optical properties of ZnO:Tb thin films J. Appl. Phys. 100, 053507 (2006); http://dx.doi.org/10.1063/1.2227268 (5 pages) Online Publication Date: 7 September 2006
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The influence of annealing on the morphological, structural, and optical properties of ZnO:Tb thin films on Si substrate grown by magnetron cosputtering is investigated. It has been found that the ZnO:Tb thin films with structures of tetrapod and screwlike nanorod are formed after annealing at temperature of 950 °C. X-ray photoelectron spectroscopy, energy dispersive spectroscopy, and Raman analyses prove that the tetrapod-aiguille zinc oxide (T-A-ZnO) and the screwlike nanorods are composed of Zn, Tb, and O elements. The photoluminescence spectra of the ZnO:Tb thin films with the T-A-ZnO structure and the screwlike nanorods are featured with two ultraviolet emission peaks and one strong green emission band, and the photoluminescence intensity increases with increasing annealing temperature. The surface defects in the T-A-ZnO structure and the screwlike nanorods are considered to be responsible for enhanced green emission in the annealed ZnO:Tb thin films.
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Nanoscale studies of domain wall motion in epitaxial ferroelectric thin films J. Appl. Phys. 100, 051608 (2006); http://dx.doi.org/10.1063/1.2337356 (10 pages) Online Publication Date: 13 September 2006
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Atomic force microscopy was used to investigate ferroelectric switching and nanoscale domain dynamics in epitaxial Pb(Zr0.2Ti0.8)O3 thin films. Measurements of the writing time dependence of domain size reveal a two-step process in which nucleation is followed by radial domain growth. During this growth, the domain wall velocity exhibits a v∝exp−(1/E)μ dependence on the electric field, characteristic of a creep process. The domain wall motion was analyzed both in the context of stochastic nucleation in a periodic potential as well as the canonical creep motion of an elastic manifold in a disorder potential. The dimensionality of the films suggests that disorder is at the origin of the observed domain wall creep. To investigate the effects of changing the disorder in the films, defects were introduced during crystal growth (a-axis inclusions) or by heavy ion irradiation, producing films with planar or columnar defects, respectively. The presence of these defects was found to significantly decrease the creep exponent μ, from 0.62–0.69 to 0.38–0.5 in the irradiated films and 0.19–0.31 in the films containing a-axis inclusions.
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