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It is crucial to better understand the magnetization reversal process between soft and hard magnets and to achieve a high maximum energy product in thick composite multilayers. In this study, we find that the exchange interactions dominate in soft–hard-magnetic composite bilayers, while dipole interactions are predominant in soft–hard-magnetic composite trilayers. Based on the first-order reversal curve, magnetization reversal models are developed for both the thick composite bilayer and trilayer. Dipole interactions play an important role in the long range, resulting in higher coercivity and remanence in the thick trilayer. A multilayer in a stacked trilayer structure is achieved, which is composed of thick films with a perpendicular magnetic anisotropy at a thickness of up to 16 μm. The enhanced dipole interactions lead to a remanent polarization of 1 T and a maximum energy product of 22.5 MGOe. This work contributes to the preparation of thick films with a high maximum energy product for applications in magnetic microelectromechanical systems. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) was utilized to measure the valence band offset (ΔEV) of the TiZnSnO (TZTO)/Si heterojunction. TZTO films were deposited on Si (100) substrates using magnetron sputtering at room temperature. By using the Zn 2p3/2 and Sn 3d5/2 energy levels as references, the value of ΔEV was calculated to be 2.69 ± 0.1 eV. Combining with the experimental optical energy band gap of 3.98 eV for TZTO extracted from the UV-vis transmittance spectrum, the conduction band offset (ΔEC) was deduced to be 0.17 ± 0.1 eV at the interface. Hence, the energy band alignment of the heterojunction was determined accurately, showing a type-I form. This will be beneficial for the design and application of TZTO/Si hybrid devices. [ABSTRACT FROM AUTHOR]

We have investigated the influence of ZnO orientation on the valence band offset (ΔEV) of Mg0.2Ni0.8O(111)/ZnO (1120) and Mg0.2Ni0.8O(111)/ZnO(0002) heterostructures by x-ray photoelectron spectroscopy. Combining with the experimental optical energy band gap extracted from UV-vis transmittance spectra, the energy band alignment at the interfaces has been determined. The ΔEV has been found to be 1.8 ± 0.1 eV and 1.4 ± 0.1 eV for Mg0.2Ni0.8O(111)/ZnO (1120) and Mg0.2Ni0.8O(111)/ZnO(0002), respectively. Both the heterostructures show type-II band configurations with conduction band offsets (ΔEC) of 2.4 ± 0.1 eV and 2.0 ± 0.1 eV, respectively. The ZnO orientation correlated electronic structure in p-Mg0.2Ni0.8O/n-ZnO interfaces can be explained well by the effect of spontaneous polarization in ZnO. Furthermore, the results offer opportunity that desired band offsets in MgxNi1-xO/ZnO heterostructures can be obtained by appropriately adjusting Mg composition. [ABSTRACT FROM AUTHOR]

The two-step freezing and melting of the field-induced ferroelectric order in PbMg1/3Nb2/3O3 (PMN) and (PbMg1/3Nb2/3O3)0.88(PbTiO3)0.12 (PMN-PT) is investigated. In PMN-PT, direct microscopic images show that both steps occur in the same spatial regions. The higher temperature freezing corresponds to the higher temperature melting, indicating that the stages are not just kinetically but also thermodynamically distinct. The higher-T melting step shows several indications of being a sharp first-order transition near an equilibrium temperature. The lower-T melting step shows more kinetic dependence. Partially poled PMN also spontaneously approaches saturation polarization on zero-field aging, indicating that the true equilibrium state is ferroelectric below ∼200 K. In PMN-PT, a variety of kinetic measurements on the ferroelectric state indicate that the kinetics are governed by a glassy matrix showing aging effects. [ABSTRACT FROM AUTHOR]

The microstructure and crystal orientations of polycrystalline films crucially affect the properties and performance of the films. Controlling preferred orientations (PO) and related film morphology are necessary to obtain the desirable properties. In this paper, we demonstrate a rational and effective route toward the realization of non-polar p-type ZnO thin film with surface texture on quartz substrate through Mn-Na codoping. It is uncovered experimentally and theoretically that mono-doping of Mn creates opportunity to realize PO from polar (c-axis) to non-polar ([formula], [formula], and [formula]) changing. With Mn-Na codoping, an acute modulation of the growth behavior and electrical conductivity of the film have been revealed, leading to weak p-type non-polar Zn0.94Mn0.05Na0.01O (ZMNO) texture. The dominant mechanism for the non-polar self-texture in the current paper is deliberately elucidated as resulting from the interplane surface diffusion with the cooperative effect of impurity dopants. The ZMNO films exhibit p-type conduction with hole concentration of 9.51 × 1015-1.86 × 1017 cm-3 and enhanced room temperature (RT) ferromagnetism possessing a saturation magnetization (Ms) of 1.52 μB/Mn. The results have potential applications in development of non-polar optoelectronic devices such as lighting emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

The interaction of Na impurities and O vacancies (VO) in ZnO was studied in theory and experiment. The VO facilitated substitutional Na (NaZn/NaZn-) acceptors with inhibiting interstitial Na (Nai/Nai+) donors, which may benefit the p-type conductivity. The formed (NaZn-VO)+/0 complexes induced the change of band structures of ZnO, with the broadening of gap energies and disappearance of the VO2+-related impurity level, which confirmed by the blue shift of the near-band-edge (NBE) UV emission and the decay of the visible emission in PL spectra. The strong and dominant NBE UV emission suggested acceptable luminescence behaviors of Na-doped ZnO. [ABSTRACT FROM AUTHOR]

High quality Zn0.92Cd0.08O/ZnO multiple quantum wells with smooth interfaces have been prepared on c-plane sapphire substrates by pulsed laser deposition. The periodic structure has been characterized by scanning transmission electron microscope and energy dispersive x-ray spectroscopy line scans. The temperature dependent photoluminescence of Zn0.92Cd0.08O/ZnO exhibits an inconspicuous S-shaped property due to a combined effect of the slightly disordered ZnCdO alloy. We can observe both quantum confinement effects and quantum-confinement Stark effect in the quantum wells. We can modulate the well emission energy from 2.90 to 3.085 eV by varying the well thickness at room temperature. [ABSTRACT FROM AUTHOR]

The microscopic piezoelectric response and ferroelectric domain switching in the (001)-oriented rhombohedral piezo-/ferroelectric (1 - x)Pb(Sc1/2Nb1/2)O3 - xPbTiO3 (PSN-PT) and relaxor Pb(Sc1/2Nb1/2)O3 (PSN) single crystals were studied by piezoresponse force microscopy. PSN-PT shows clear domain structures while the domain contrast of PSN is very weak. For PSN-PT, after being fully poled vertically, its lateral domain structure is still composed of a multi-domain state. Both PSN-PT and PSN crystals respond to positive and negative DC field drives through piezoelectricity. However, their poling behaviors are different. For PSN-PT, during successive applications of a positive external electric field, the areas with piezoresponse in phase with the electric field grow at the expense of domains of opposite piezoresponse, implying a domain switching process via sideway motion of domain walls. On the other hand, in the PSN single crystal, the piezoresponse contrast of the alternatively poled area shows a uniformly fading and enhancing pattern, depending on the direction of the polarization component of the domains relative to the external field. While the domain pattern of PSN-PT and its evolution under an external field behave like a normal ferroelectric material, the domain structure and domain evolution process of PSN appear to be abnormal for a ferroelectric, but consistent with the character of a relaxor. [ABSTRACT FROM AUTHOR]

We propose a specifically designed structure to fabricate thin-film transistors using amorphous indium-gallium-zinc-oxide (a-IGZO) films as the active channel layers. The I-shaped gate electrode is employed to define the channel width, reducing overlaps between the gate and source/drain electrodes. The devices with such a structure exhibit acceptable electrical performance and stability after annealing treatment. The XPS data show that the as-deposited a-IGZO film has not a very dense structure that may induce shallow traps. A shallow trap model is proposed to explain the large threshold voltage shifts of the as-deposited device. Annealing treatment can eliminate these shallow traps and improve the device stability. [ABSTRACT FROM AUTHOR]

Microwave (8.43 GHz) absorption properties have been measured for multiwalled carbon nanotube (MWCNT)-epoxy composites. A microwave resonant cavity technique was utilized as a probe. Six groups of MWCNT-epoxy composite samples with different MWCNT outside diameters were fabricated and tested. The weight percentages of MWCNTs in each sample group were in the range of 1%-10%. The amplitudes of the absorption profiles, the linewidths at half-power maxima, and the shifts in resonant frequencies under load for the six groups of MWCNT-epoxy composite samples were compared. Similar to our previous results measured at 9.968 GHz [Z. Ye et al., J. Appl. Phys. 108, 054315 (2010)], the microwave absorption properties of our samples strongly rely on two parameters: the number of nanotubes and the density of nanotube bundles. It was found that the measured microwave absorption properties of the samples around 8.43 GHz showed a more sensitive response to the magnetic component of the microwave field rather than the electric component. [ABSTRACT FROM AUTHOR]

The broadband gigahertz dynamics of a relaxor ferroelectric crystal 0.70Pb(Sc1/2Nb1/2)O3-0.30PbTiO3 with a composition close to the starting point of the morphotropic phase boundary is studied by Brillouin scattering. The significant anomaly of the longitudinal acoustic (LA) mode is observed in the vicinity of the Curie temperature, TC = 500 K. Upon cooling, it starts below the Burns temperature, TB = 670 K, due to the interaction between the LA mode and dynamic polar nanoregions (PNRs). The broad central peak (CP) clearly appears below TB, and its intensity becomes a maximum at TC. The relaxation time, τCP, determined from the CP width, shows the typical critical slowing down of the order-disorder phase transition in the vicinity of TC. The size of a dynamic PNR significantly increases below the intermediate temperature, T* = 562 K. [ABSTRACT FROM AUTHOR]

Polarization switching in ergodic relaxor and ferroelectric phases in the PbMg1/3Nb2/3O3–PbTiO3 (PMN-PT) system is studied using piezoresponse force microscopy, single point electromechanical relaxation measurements, and voltage spectroscopy mapping. The dependence of relaxation behavior on voltage pulse amplitude and time is found to follow a universal logarithmic behavior with a nearly constant slope. This behavior is indicative of the progressive population of slow relaxation states, as opposed to a linear relaxation in the presence of a broad relaxation time distribution. The role of relaxation behavior, ferroelectric nonlinearity, and the spatial inhomogeneity of the tip field on hysteresis loop behavior is analyzed in detail. The hysteresis loops for ergodic PMN-10%PT are shown to be kinetically limited, while in PMN with larger PT content, true ferroelectric hysteresis loops with low nucleation biases are observed. [ABSTRACT FROM AUTHOR]

Composites containing pure, uniform, and well-dispersed ferroelectric barium titanate (BaTiO3) nanocrystallites with various particle sizes as active phase and polyvinylidene fluoride (PVDF) polymer as matrix are fabricated using a two-step mixing and hot-pressing technique. The dependences of the dielectric and ferroelectric properties of the as-prepared composites on the nanoparticle sizes are investigated systematically. The polarization-electric field hysteresis loops are displayed, indicating the ferroelectricity for the BaTiO3/PVDF nanocomposites. The remanent polarization is found to increase as the size of BaTiO3 particles increases from 25 to 500 nm. The dielectric constant of the composites exhibits a complex variation as a function of the BaTiO3 nanoparticle sizes: it reaches a maximum value in the composites with BaTiO3 nanoparticle sizes of 80–100 nm and decreases again when the particle size is further reduced under 50 nm. [ABSTRACT FROM AUTHOR]

A solution chemical method utilizing ethylene glycol as solvent has been developed to prepare the ceramics of (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3[(1-x)PMN–xPT] from a precursor powder that can be pressed and fired in one step to produce high quality ceramics with excellent piezoelectric properties. The ceramics reach a relative density of up to 97% of the theoretical value after direct calcinations. This high density is achieved without the need of additional sintering after calcination which is usually required in conventional solid state syntheses to produce ceramics. The ceramics exhibit a unipolar piezoelectric coefficient d33 of 848 pC/N, which is one of the highest values for any unmodified/untextured binary systems reported to date. Since the piezoelectric properties depend on composition and electric field, the effect of poling conditions was investigated. A critical temperature limit has been found, above which poling can dramatically impair the piezoelectric properties due to a field-induced increase in the monoclinic phase component around the morphotropic phase boundary. [ABSTRACT FROM AUTHOR]

This work investigates the photoluminescence properties of ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs), which have been fabricated by pulsed-laser deposition on (111) Si substrates using intervening epitaxial Lu2O3 buffer layers. In ZnO/Zn0.9Mg0.1O MQWs, the luminescence is dominated by localized exciton (LE) emission throughout the whole temperature range studied. With increasing temperature from 10 to 300 K, the LE emission redshifts by 38 meV. This redshift is believed to be due to the thermalized excitons occupying higher-lying localized states where they emit higher energy radiation and temperature-induced band gap shrinkage. Moreover, the LE emission from the MQWs decays more slowly than exciton emission from ZnO. In addition, the LE emission in the MQWs shows a systematic blueshift with decreasing well width, which is consistent with a quantum size effect. [ABSTRACT FROM AUTHOR]

Hydrogen is codoped with sodium into ZnO films. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy indicate that the Na concentration decreases as the substrate temperature increases. Hall-effect tests reveal a transition from n-type to p-type conduction when the growth temperature increases, which is explained by the suppression of Na interstitials by codoping with H and Na of appropriate concentrations. An insulating intended Na–H codoped sample shows reduced resistivity and p-type conductivity after annealing at 550 °C, which may be due to dissociation of NaZn–H complexes. The realization of p-type ZnO by Na–H codoping may explain the discrepancies in behavior of Na in ZnO and suggests the potential of Na–H codoping method [E.-C. Lee and K. J. Chang, Phys. Rev. B 70, 115210 (2004)]. [ABSTRACT FROM AUTHOR]

We investigated optical properties of Sb-doped p-type ZnO films grown on n-Si (100) substrates by oxygen plasma-assisted pulsed laser deposition. Two acceptor states, with the acceptor levels of 161 and 336 meV, are identified by well-resolved photoluminescence spectra. Under oxygen-rich conditions, the deep acceptor in Sb-doped ZnO film is Zn vacancy. The shallow acceptor is SbZn-2VZn complex induced by Sb doping. The origin of p-type behavior in Sb-doped ZnO has been ascribed to the formation of SbZn-2VZn complex. [ABSTRACT FROM AUTHOR]

Resistance-voltage curves of n-on-p Hg1-¿CdxTe long-wavelength infrared photodiodes forming 128-element array are measured in the temperature range of 40¿150 K. Experimentally obtained characteristics are fitted by the simultaneous-mode nonlinear fitting program. The dark current mechanisms induced by diffusion, generation recombination, trap-assisted tunneling, band-to-band tunneling, and series resistance effect are included in the physical model for R-V curve fitting. Six characteristic parameters as function of temperature are extracted from measured R-V curves. The characteristics of extracted current components at low temperatures indicate significant contributions from tunneling effects, which is the dominant leakage current mechanism for reverse bias greater than approximately 50 mV. The Hg-vacancy-induced acceptor trap tends to invert to donor type at higher temperature, typically larger than 120 K, while it can maintain stable at the temperature of 60¿40 K. The stable temperature of ion-implantation-induced traps is about 90¿60 K, which possibly tends to be ionized at high temperature. However, a low operation temperature can induce the frozen effects of the ion-implantation-induced donor traps. Fitting certainty analysis shows that the error of one parameter can be magnified when one of the other types of dark current mechanisms dominates the dark current and is even infinitely enlarged under large reverse bias. The different bias regions at which each fitting parameter has the largest influence to the R-V curve should be ascertained. The results of the present work demonstrate that modeling of the dynamic resistance in small voltage range or at just operation temperature are insufficient for determining the mechanism of carrier transport across the Hg1-¿CdxTe junction and a detailed theoretical study of the current-voltage characteristics in wider voltage range or at... [ABSTRACT FROM AUTHOR]

Dislocations in the ZnMgO pleated nanosheets were observed from high-resolution transmission electron microscopy (TEM). The Burgers vector was identified as [formula] from the Fourier filtered TEM images. Raman spectra revealed that there were microstructure defects in the ZnMgO nanosheets with the increasing Mg content. The incorporation of the Mg impurities in the ZnMgO nanosheets may promote the congregation of oxygen vacancies and thus facilitate the generation of dislocations. The oxygen deficiency as well as surface dislocations played an important role in determining the optical properties of ZnMgO pleated nanosheets. [ABSTRACT FROM AUTHOR]

Temperature-dependent photoluminescence (PL) spectroscopy is employed to investigate the effects of exposure to ambient air on the optical property of Al-doped ZnO nanorods. Low temperature PL of the as-grown nanorods shows dominant D0X (excitons bound to neutral donors) emission at 3.363 eV and surface state-related emission at 3.310 eV. After exposure to ambient air, both of them vanish and the first LO phonon replica of free exciton is observed instead. It is proposed that surface adsorption and indiffusion of oxygen in ambient air result in surface modification and destruction of D0X complex. [ABSTRACT FROM AUTHOR]

P-doped p-type ZnO thin films have been grown by metalorganic chemical vapor deposition. By modulating the P evaporating temperature, p-type conductivity can be controlled due to the different P content incorporated into the ZnO films. The P-doped p-type ZnO thin films are of high optical quality, as indicated by low-temperature photoluminescence. P-related acceptor state with an energy level of 163 meV is identified from free-to-neutral-acceptor transitions. In addition, x-ray photoelectron spectroscopy confirms that only one chemical bonding state of P exists in the P-doped ZnO thin films. [ABSTRACT FROM AUTHOR]

We propose a theoretical model based on the concept of multiferroic tunnel junction. The model is capable of producing eight different logic states by combining the spin-filter effect and the screening of polarization charges between two electrodes through a general spintronic tunneling. The dependence of the conductance ratio with very large magnitude on electric polarization, exchange splitting, barrier width, and bias voltage is investigated. The result may provide some insights into the realization of octal data storage (namely, the eight different logic states are used as octal code), which could lead to the tremendous increase of memory storage density. [ABSTRACT FROM AUTHOR]

Temperature-dependent photoluminescence excitation (PLE) spectroscopy is used to study nominally undoped and indium-doped ZnO nanorods grown by thermal evaporation method. Clear differences in PLE features between the two samples are observed. We demonstrate that the first derivative of the PLE spectra can be used to determine the free exciton energy for both samples. The physics behind is understood either in terms of competing absorption and recombination to the green emission band being monitored, or based on the analogy between the first derivative of PLE and photoreflectance spectroscopy. Two residual donor levels located at about 37 and 120 meV below the conduction band minimum are identified from the PLE spectra. [ABSTRACT FROM AUTHOR]

The (1-x)BaTiO3–xBaSnO3 (0≤x≤0.30) perovskite solid solution ceramics were prepared by solid state reaction and studied by dielectric spectroscopy. The complex dielectric permittivity was measured as a function of frequency (0.1 Hz–100 kHz) in the temperature (T) range of 123–573 K. The transition from the high-temperature paraelectric state where the dielectric constant obeys the Curie-Weiss law to the ergodic cluster state is found to occur at the same temperature of 485 K in all the compositions of x>=0.04 and at lower temperatures in those with a smaller x. For 0≤x≤xc=0.19, the temperature of the dielectric peak Tm, corresponding to the diffuse transition from the ergodic polar cluster state to the ferroelectric state, decreases with increasing x and does not depend on frequency. The diffuseness of the peak gradually increases. For x>xc, the permittivity exhibits relaxor behavior with the frequency-dependent Tm satisfying the Vogel-Fulcher law. The temperature variation of the permittivity on the high-temperature slope of the peak (T>Tm) is characterized by the characteristic Lorenz-type quadratic law for relaxors, with the diffuseness increasing with the increase of x. The mechanisms of the dielectric response in different parts of the phase diagram are discussed. In particular, the crossover from diffuse ferroelectric phase transition to relaxor ferroelectric behavior is attributed to the appearance at x>xc of the additional dielectric contribution arising from the flipping of the local polarization of the polar clusters. The temperature-composition phase diagram of the Ba(Ti1-xSnx)O3 system has been established, which delimits the paraelectric, ergodic polar cluster, nonergodic ferroelectric, and relaxor phases (states) and indicates the crossover from ferroelectric to relaxor behavior at x=xc. [ABSTRACT FROM AUTHOR]

Al-doped ZnO (AZO) thin films have been prepared by mist chemical vapor deposition and magnetron sputtering. The band gap shift as a function of carrier concentration in n-type zinc oxide (ZnO) was systematically studied considering the available theoretical models. The shift in energy gap, evaluated from optical absorption spectra, did not depend on sample preparations; it was mainly related to the carrier concentrations and so intrinsic to AZO. The optical gap increased with the electron concentration approximately as ne2/3 for ne≤4.2×1019 cm-3, which could be fully interpreted by a modified Burstein–Moss (BM) shift with the nonparabolicity of the conduction band. A sudden decrease in energy gap occurred at 5.4-8.4×1019 cm-3, consistent with the Mott criterion for a semiconductor-metal transition. Above the critical values, the band gap increased again at a different rate, which was presumably due to the competing BM band-filling and band gap renormalization effects, the former inducing a band gap widening and the latter an offsetting narrowing. The band gap narrowing (ΔEBGN) derived from the band gap renormalization effect did not show a good ne1/3 dependence predicated by a weakly interacting electron-gas model, but it was in excellent agreement with a perturbation theory considering different many-body effects. Based on this theory a simple expression, ΔEBGN=Ane1/3+Bne1/4+Cne1/2, was deduced for n-type ZnO, as well as p-type ZnO, with detailed values of A, B, and C coefficients. An empirical relation once proposed for heavily doped Si could also be used to describe well this gap narrowing in AZO. [ABSTRACT FROM AUTHOR]

Modeling of the hysteresis loop of ferroelectric thin films has been thought very difficult owing to its nonlinear and history-dependent electric field effects. Here we extend the Preisach model [Z. Phys. 94, 277 (1935)] by using the distribution function integral and superposition method. The model shows improved hysteresis loop that agrees reasonably well with the experimental data measured from the bismuth layer-structured ferroelectric thin films. Compared with the previous model, the current model provides polarization-field (P-E) loop with full and symmetric shape, suitable coercive field (Ec), and few undesirable parameters. The butterfly loop of perovskite-type ferroelectric thin films is also simulated. Additionally, the approach is able to describe the unsaturated loops obtained under various ac electric fields, which is very useful in circuit simulation of ferroelectric field effect transistor or ferroelectric capacitor. [ABSTRACT FROM AUTHOR]

A data-processing approach has been developed to obtain device parameters from resistance-voltage (R-V) curves measured on long-wavelength HgCdTe n-on-p photodiodes. The physical model used for R-V curve fitting includes the dark current mechanisms induced by diffusion, generation recombination, trap-assisted tunneling, and band-to-band tunneling. Moreover, the series resistance effect is also taken into account. Six parameters, which include the dopant density Nd in the n region, the ratio of mobility to lifetime of electrons μn/τn in the p region, the effective lifetime τ0 in the depletion region, the relative energy position of trap level Et/Eg and its density Nt in the depletion region, and the series resistance Rs, can be extracted from measured R-V curves. The fitting procedure has been presented in detail and the error ranges of the extracted parameters have been discussed. By fitting to the R-V characteristics of three long-wavelength devices with different Cd compositions, the applicability of our data-processing approach has been verified for obtaining those basic parameters. [ABSTRACT FROM AUTHOR]

(Zn,Al)O thin films have been prepared by a dc reactive magnetron sputtering system with the Al contents in a wide range of 0–50 at. %. The structural, optical, and electrical properties of (Zn,Al)O films were detailedly and systematically studied. The amount of Al in the film was nearly the same as, but often lower than, that in the sputtering target. The growth rate of films monotonically decreased as the Al content increased. In a low Al content region (<10 at. %), Al-doped ZnO (AZO) thin films could be obtained at 400 °C in an Ar–O2 ambient with good properties. The optimal results of n-type AZO films were obtained at an Al content of 4 at. %, with low resistivity ∼10-4 Ω cm, high transmittance ∼90% in the visible region, and acceptable crystal quality with a high c-axis orientation. The band gap could be widened to 3.52 eV at 4 at. % Al due to the Burstein-Moss shift [E. Burstein, Phys. Rev. 93, 632 (1954)] modulated by many-body effects. An appropriate Al-doping concentration served effectively to release the residual, compressive stress in film, which may be the reason for the improvement in film stability and the increment in grain size as well. In a medium Al content region (10–30 at. %), however, the film quality was degraded, which was presumably due to the formation of clusters or precipitates in the grains and boundaries. Besides the (002) plane, other diffraction peaks such as (100) and (101) planes of ZnO were observed, but the (Zn,Al)O films still exhibited a single-phase wurtzite ZnO structure. An intragrain cluster scattering mechanism was proposed to interpret the reduction of carrier mobility in films with the Al contents in the 7–20 at. % region. The solubility limit of Al in ZnO film was identified to be in the 20–30 at. % range, much higher than the thermodynamic solubility limit of 2–3 at. % in ZnO. In a high Al content region (>=30 at. %), there were distinct observations for (Zn,Al)O films. As the Al content was 30 at. %, the film appeared in a two-phase nature with ZnO hexagonal and Al2O3 rhombohedral structures. At the 50 at. % Al content, the matrix of the (Zn,Al)O film was Al2O3, and no evident trace of wurtzite ZnO was observed. The electrical and optical properties for both cases were also very different from those at the Al contents below 30 at. %. [ABSTRACT FROM AUTHOR]

The dependence of lattice strain in Al-N codoped p-type ZnO films on Al content and growth temperature was investigated. With increasing Al content, the compressive strain in the film first increases and then decreases. We suggest that the strain decrease is due to the occupation of more substitutional sites by Al at relatively high Al content, which partially compensates the compressive strain. Reversion of conduction type at high Al content and high temperature was also observed. By studying the strain and electrical properties of the codoped films, we conclude that ZnO film should be grown at intermediate temperatures and with low Al content to achieve both good p-type conduction and reasonable crystal quality. The compressive strain results in increase of the optical band gap, and a linear relationship between them was obtained. [ABSTRACT FROM AUTHOR]

We report on the photoluminescence (PL) properties of quasialigned ZnCdO single-crystal nanorods prepared by thermal evaporation of Zn and CdCl2 on a Si substrate using Au as a catalyst. The temperature-dependent PL spectra of the ZnCdO nanorods show that each spectrum displays an intense near-band-edge (NBE) emission around 3.1 eV, as well as a weak defect-related band around 2.5 eV. At low temperatures, the NBE band consists of three peaks at 3.23, 3.16, and 3.06 eV. From time-integrated and time-resolved PL analyses, we suggest that the peak at 3.06 eV is associated with carriers localized at potential minima induced by the Cd spatial inhomogeneous distribution in ZnCdO alloys. The peak at 3.16 eV is attributed to the excitonic emission of ZnCdO, while the peak at 3.23 eV is ascribed to bound excitons in ZnO. [ABSTRACT FROM AUTHOR]

The domain structure of (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals with composition x≈0.33 in the range of the morphotropic phase boundary (MPB) was studied. Based on the analysis of spontaneous strain compatibility and charge of domain walls, we have established the permissible domain arrangements for the ferroelectric phases of different symmetries, which are expected to occur in the range of the MPB. Examination of (001)-oriented unpoled and electrically poled (along the [001] direction) crystal plates in a polarizing microscope reveals a monophase state with the domain structure compatible with the structure theoretically predicted for the MC monoclinic phase (space group Pm), which was recently discovered in the compositions close to the MPB by x-ray and neutron diffraction studies. In the unpoled crystal, the 180° walls between the domains whose spontaneous polarization vectors are parallel to the plane of the crystal plate (i.e., a-domains) are observed. The domain structure of the poled crystal is predominantly composed of crystallographically prominent Wf walls parallel to (001) (i.e., the plane of the crystal plate) and inclined S walls parallel to [110] or [110] direction. In poled and unpoled samples, an optical rotatory polarization effect is found, which is related to the inhomogeneity of the sample resulting from the mixture of domains. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A resonant microwave cavity operating in the TM010 mode was used to determine the microwave susceptibility of single walled carbon nanotubes (SWNT) that are blended in polymer matricies. The frequencies of the probe signal were 9.8, 11.4, and 35.93 GHz. Samples of 3%–19% blends of SWNT in polycarbonate were tested to determine the best blends for shielding of devices from microwaves at these frequencies. It appears that blends of 9%–11% are very effective in shielding the electric vector of electromagnetic waves. Both the electric vector and the magnetic vectors were probed by the process to determine the nature of coupling between the SWNTs and the applied fields. Some details are given about the apparatus design that enables computer collection and processing of the data to be achieved. An electronic differentiation technique was used to allow the second derivative of the cavity absorption profile to be displayed for precise measurement. Data are presented to show the relative microwave absorption for different blends of the SWNTs with polycarbonates. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ac losses in three disk-shaped YBa[sub 2]Cu[sub 3]O[sub 7] (YBCO) films, which were deposited on SrTiO[sub 3] by the pulsed-laser-deposition technique and had thicknesses, d, of 0.2, 1.0, and 3.0 μm, were measured in perpendicular applied ac magnetic fields to ∼0.14 T at 10 Hz in liquid nitrogen. The losses at low fields were found to be a strong function of the film thickness. The measured losses were compared with the theoretically calculated losses. The ac losses calculated using a field-independent critical-current density, the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 50, 9355 (1994)], agreed very well with the 0.2-μm-thick film, while the calculated losses agreed well with the measured ones when a field-dependent critical-current density, the Kim model [D. V. Shantsev, Y. M. Galperin, and T. H. Johansen, Phys. Rev. B 61, 9699 (2000)], was used for the films of thickness 1.0 and 3.0 μm. However, a surprising discrepancy was found in the values of B[sub c] and B[sub 0] for thinner YBCO films depending on whether they were determined by ac or dc measurements. B[sub c] is defined as B[sub c]=μ[sub 0]J[sub c](0)d/2, B[sub 0] is the characteristic field in the Kim-model critical-current density J[sub cK](B[sub a])=J[sub c](0)/(1+B[sub a]/B[sub 0]), and J[sub c](0) is the critical-current density at applied magnetic field B[sub a]=0. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ac losses at 20 and 30 Hz were measured for two disk-shaped YBa[sub 2]Cu[sub 3]O[sub 7] films in perpendicular peak applied magnetic fields up to ∼0.2 T in liquid nitrogen. One of the films had a significantly higher critical-current density than the other as determined from the loss measurements. Also, it exhibited a more-uniform flux penetration around the circumference of the disk than the other as observed by magneto-optical images of these films in perpendicular dc fields. The results from this film were compared with theoretical predictions of ac losses for disks of thin superconducting films in perpendicular magnetic fields using the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 55, 9355 (1994)], and the Kim critical-current model [D. V. Shantsev et al., Phys. Rev. B 61, 9699 (2000)]. The asymptotic Bean model predictions for low and high fields were in reasonably good agreement with the data. The numerical calculation of the losses following Shantsev et al. was found to give extremely good agreement with the loss data throughout the entire field range of the measurement when the Kim model for the critical-current density was used. [ABSTRACT FROM AUTHOR]

Silver-doped SrBi[sub 2]Ta[sub 2]O[sub 9] (Ag:SBT) ceramics were synthesized by solid state reactions. The reaction mechanism has been deduced based on the crystal defect chemistry. It involves the diffusion of Ag[sup +] and O[sup 2-] ions into the (Bi[sub 2]O[sub 2])[sup 2+] layers between the perovskite-like units to recover the bismuth and oxygen vacancies, respectively, which were inherently present in SBT ceramics due to the volatilization of Bi[sub 2]O[sub 3] at high temperatures. The Ag:SBT samples have been characterized by a variety of techniques: x-ray diffraction, dielectric and ferroelectric measurements, and impedance spectroscopy. Ag doping is found to significantly affect the structural and physical properties of SBT, including lattice parameters, Curie temperature, bulk conductivity, activation energy, and ferroelectricity. These effects have been interpreted based on the model of the recovery of oxygen and bismuth vacancies upon Ag doping. The effects of Ag diffusion should be taken into account when using Ag as electrode materials for the characterization of the electric properties of SBT and related materials. [ABSTRACT FROM AUTHOR]

Unipolar electric field-induced strain was studied in the [001][sub cub]-oriented 0.65Pb(Mg[sub ⅓]Nb[sub 2/3])O[sub 3]-0.35PbTiO[sub 3] crystals with the composition close to the morphotropic phase boundary, which are known to show enhanced piezoelectric properties. Polarized-light microscopy was used to study the domain structure. In the samples containing the mixture of rhombohedral and tetragonal ferroelectric phases, a giant electrostrictive effect was found to exist after poling, in addition to the piezoelectric effect. The a domains of the tetragonal phase with polarization perpendicular to the poling field were observed. Their existence in the poled crystals is due to the elastic interactions with the rhombohedral domains. The electromechanical response of the tetragonal a domains, which should be purely electrostrictive due to the crystal symmetry, is suggested to provide the intrinsic contribution to the observed electrostriction. The extrinsic contribution to electrostriction is explained by the 90° reorientation of the a domains into the c domain state. Upon application of the driving field, the onset of extrinsic electromechanical response was found to follow the stretched exponential relaxation pattern. [ABSTRACT FROM AUTHOR]

Substitutions by aliovalent cations on the Sr[sup 2+] and Bi[sup 3+] sites of ferroelectric SrBi[sub 2]Ta[sub 2]O[sub 9] (SBT) have been carried out, which result in modified dielectric and electrical properties of SBT. The substitution of 10 mole % Fe[sup 3+] for Sr[sup 2+] shows an increase of 80 °C in T[sub C], whereas Ca[sup 2+] substitution for Bi[sup 3+] gives rise to diffused and frequency dispersive dielectric maxima with a relaxor-like behavior. The presence of Ca[sup 2+] in the (Bi[sub 2]O[sub 2])[sup 2+] layers appears to enhance the mobility of charge carriers thus increasing the bulk conduction of the sample. On the other hand, Fe[sup 3+] addition in the perovskite-like units results in a sharp dielectric anomaly at the ferroelectric phase transition, with a bulk conductance similar to that of pure SBT compound, but with a reduced space charge relaxation time. The low temperature conductivity mechanism shows a frequency dependence, which can be ascribed to the space charge mainly due to the oxygen vacancies. The dielectric and conductivity properties of the Ca[sup 2+]-doped SBT make it a promising material for the fatigue resistance in device applications. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Provides information on a study which analyzed the domain structures and phase transitions of piezo/ferroelectric single crystals by polarized light microscopy. Details on the experiment; Crystal optical principle; Results and discussion.

We report ferrimagnetism and reentrant relaxor ferroelectricity near room temperature in a Yb-doped PbFe2/3W1/3O3 cubic perovskite. Structural analysis reveals the presence of a single cubic perovskite phase, with the Fm 3 ¯ m space group [lattice parameter: a = 8.0112(3) Å], and partial B-site ordering. The B-site ordering yields uncompensated magnetic moments in the antiferromagnetic structure of PbFe2/3W1/3O3 and ferrimagnetism near room temperature. An excess moment of ∼0.6 μB/B-site may be estimated from magnetic hysteresis curves recorded up to 50 kOe at 5 K. The temperature dependent magnetodielectric study reveals a sequential phase transition from a long-range ferroelectric state (across 280 K) to a short-range relaxor ferroelectric state (across 190 K). The long-range ferroelectric ordering is found to be more affected by the application of external magnetic fields than the relaxor phase. [ABSTRACT FROM AUTHOR]

The recombination property of nitrogen (N)-related acceptor-bound states in ZnO has been investigated by photoluminescence (PL), time-resolved PL, and selective PL. Several possible recombination processes were discussed by analyzing the relaxation and recombination properties under large Coulomb interaction. It is strongly suggested that bound exciton emission dominates the recombination process related to the N acceptor. The recombination lifetime is 750 ps and the binding energy is 67 meV for N-acceptor-bound exciton at low temperature. [ABSTRACT FROM AUTHOR]

The integration of III-V on silicon is still a hot topic as it will open up a way to co-integrate Si CMOS logic with photonic devices. To reach this aim, several hurdles should be solved, and more particularly the generation of antiphase boundaries (APBs) at the III-V/Si(001) interface. Density functional theory (DFT) has been used to demonstrate the existence of a double-layer steps on nominal Si(001) which is formed during annealing under proper hydrogen chemical potential. This phenomenon could be explained by the formation of dimer vacancy lines which could be responsible for the preferential and selective etching of one type of step leading to the double step surface creation. To check this hypothesis, different experiments have been carried in an industrial 300mm metalorganic chemical vapor deposition where the total pressure during the annealing step of Si(001) surface has been varied. Under optimized conditions, an APBs-free GaAs layer was grown on a nominal Si(001) surface paving the way for III-V integration on silicon industrial platform. [ABSTRACT FROM AUTHOR]

Metal organic chemical vapor deposition of GaAs on standard nominal 300 mm Si(001) wafers was studied. Antiphase boundary (APB) free epitaxial GaAs films as thin as 150 nm were obtained. The APB-free films exhibit an improvement of the room temperature photoluminescence signal with an increase of the intensity of almost a factor 2.5. Hall effect measurements show an electron mobility enhancement from 200 to 2000 cm²/V s. The GaAs layers directly grown on industrial platform with no APBs are perfect candidates for being integrated as active layers for nanoelectronic as well as optoelectronic devices in a CMOS environment. [ABSTRACT FROM AUTHOR]

We have obtained Anti-Phase Boundary (APB) free GaAs epilayers on "quasi-nominal" (001) silicon substrates, while using a thick germanium strain relaxed buffer between the GaAs layer and the silicon substrate in order to accommodate the 4% lattice mismatch between the two. As silicon (001) substrates always have a small random offcut angle from their nominal surface plane, we call them "quasi-nominal." We have focused on the influence that this small (≤0.5°) offcut angle has on the GaAs epilayer properties, showing that it greatly influences the density of APBs. On 0.5° offcut substrates, we obtained smooth, slightly tensile strained (R=106%) GaAs epilayers that were single domain (e.g., without any APB), showing that it is not necessary to use large offcut substrates, typically 4° to 6°, for GaAs epitaxy on silicon. These make the GaAs layers more compatible with the existing silicon manufacturing technology that uses "quasi-nominal" substrates. [ABSTRACT FROM AUTHOR]

PbMg1/3 Nb2/3O3 (PMN) is a well known ferroelectric relaxor. PMN crystal doped with La3+ has greatly enlarged chemically ordered regions (CORs) in the structure. It is interesting to know how the development of CORs influences physical properties of PMN crystal. In this work, dielectric properties and distribution of relaxation times of PMN and 0.98Pb(Mg1/3Nb2/3)O3-0.02La(Mg2/3Nb1/3)O3 (PLMN) crystals are studied. The experiment was performed in 120-500 K temperature range and wide frequency range--up to 46 GHz. The results demonstrate that the relaxor behaviour of PMN and PLMN is qualitatively the same in spite of the fact that chemical ordering is very different. [ABSTRACT FROM AUTHOR]

We present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al20Sm4 phase that evolves during crystallization of an amorphous magnetron sputtered Al90Sm10 alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal. [ABSTRACT FROM AUTHOR]