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1 Sep 1998

Volume 84, Issue 5, pp. 2371-2982

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Behavior of soft piezoelectric ceramics under high sinusoidal electric fields

V. D. Kugel and L. E. Cross

J. Appl. Phys. 84, 2815 (1998); http://dx.doi.org/10.1063/1.368422 (16 pages) | Cited 30 times

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The behavior of piezoelectric, dielectric, and elastic characteristics of soft piezoelectric lead zirconate titanate (PZT) ceramics was investigated under sinusoidal electric field E applied along the poling direction and under mechanical stress-free conditions for a frequency range 10 Hz–10 kHz. Electrical displacement D3 along the poling direction, mechanical strain S1 in the direction perpendicular to the poling direction, and the resonant frequency νr of electromechanically uncoupled bending vibrations of polarized plates were measured. Commercial ceramics PZT5H, 3203HD, and PKI550 with chemical composition near the morphotropic phase boundary were used in the study. It was found that the amplitude and phase of the first harmonic of the relative strain S1(1)/Em and of the relative electrical displacement D3(1)/Em increase similarly with increasing amplitude Em of the electric field if the amplitude is less than coercive field. The corresponding increase in the square of the resonant frequency is more moderate. The dependencies are described well by linear functions except for low electric fields. The functions S1m(1)/Em and D3m(1)/Em demonstrate frequency dispersion as well. Relative amplitude of the second harmonic of the electrical displacement, D3m(2)/D3m(1), which is polar, also increases almost linearly with increasing Em. The relative third harmonic D3m(3)/D3m(1) demonstrates saturationlike behavior. By means of the electric pulse technique, it was found that irreversible changes in the remnant polarization take place even at electric fields much smaller that the coercive field. A mathematical model of a hysteretic transducer, describing the electric field dependence of electromechanical properties of soft piezoelectric PZT ceramics, was suggested. According to this approach, the response depends not only on the instantaneous magnitude of the input signal (e.g., electric field) but also on its past extreme values. It was shown that the experimental Rayleigh law is a particular case of the suggested approach. The model relates directly electric field dependencies of complex piezoelectric coefficient d31(Em) and S1(1)/Em, of complex dielectric permittivity ϵ33T(Em) and D3(1)/Em, and of the amplitude of elastic compliance s11E(Em) and νr2. Application of the model to experimental data showed that the model describes well the first three complex harmonics of D3 and the irreversible change in the remnant polarization. Physical causes of the observed behavior were analyzed. As an alternative to the model based on the 90° polarization reorientation and tetragonal/rhombohedral phase boundary motion, a new approach was suggested. In this model, the observed hysteretic changes in the electromechanical properties are assumed to be caused by the electric field dependency of the mechanical stress acting at interdomain boundaries in the partly constrained crystallites of these ceramics. © 1998 American Institute of Physics.  
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ch Permittivity (dielectric function)
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
77.22.Ej Polarization and depolarization
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis

Observation of dipole complexes in PbWO4:La3+ single crystals

Baoguo Han, Xiqi Feng, Guanqin Hu, Pingchu Wang, and Zhiwen Yin

J. Appl. Phys. 84, 2831 (1998); http://dx.doi.org/10.1063/1.368423 (4 pages) | Cited 41 times

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The frequency dependence of dielectric loss factor (tan δ) in undoped and La-doped PbWO4 crystals has been investigated over a frequency range from 10 Hz to 10 MHz and a temperature range from 40 to 370 °C. A typical dielectric relaxation phenomenon in PbWO4:La3+ has been observed. Experimental results indicate that there exist intrinsic mobile defects in pure PbWO4 crystals and lead vacancies are the predominant mobile defects. In La-doped PbWO4 crystals, La3+ ions may be located at the Pb2+ sites and combine with lead vacancies to form the dipole complexes [2(LaPb3+)•−VPb″], which may be the origin of the dielectric relaxation phenomenon in PbWO4:La3+ crystals. © 1998 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
61.72.J- Point defects and defect clusters

Pyroelectric properties of polymer dispersed ferroelectric liquid crystals

R. Bartolino, N. Scaramuzza, E. S. Barna, A. Th. Ionescu, L. A. Beresnev, and L. M. Blinov

J. Appl. Phys. 84, 2835 (1998); http://dx.doi.org/10.1063/1.368424 (6 pages) | Cited 3 times

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A polymer dispersed ferroelectric liquid crystal (PDFLC) is a novel material combining properties of a polymer (flexibility, elasticity) and ferroelectric liquid crystal (low voltage, fast electro-optical switching). Another interesting field of application of PDFLC is the detection of low intensity radiation using the pyroelectric response of the material. A PDFLC material containing a ferroelectric liquid crystal (FLC) with very high spontaneous polarization (close to 200 nC/cm2 at room temperature) was prepared to study its pyroelectric properties. The matrix was pure polymer poly-butadiene-styrene which can be mixed with liquid crystals in volatile solvents. The pyroelectric response and the spontaneous polarization were measured over a wide temperature range of the smectic C∗ phase and compared with the corresponding quantities of the pure FLC. Figures of merit of pyroelectric PDFLC films were estimated and compared with those known for conventional ferroelectrics. © 1998 American Institute of Physics.
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77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
77.22.Ej Polarization and depolarization
77.70.+a Pyroelectric and electrocaloric effects
61.30.-v Liquid crystals
77.80.-e Ferroelectricity and antiferroelectricity
64.70.M- Transitions in liquid crystals

Luminescence studies of localized gap states in colloidal ZnS nanocrystals

D. Denzler, M. Olschewski, and K. Sattler

J. Appl. Phys. 84, 2841 (1998); http://dx.doi.org/10.1063/1.368425 (5 pages) | Cited 138 times

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ZnS nanoparticles were prepared by chemical precipitation of Zn2+ with sulfur ions in aqueous solution. The ultraviolet-excited samples reveal detailed structure in the luminescence spectra. A doublet pattern observed in the long wavelength region is attributed to the coexistence of the two crystalline forms in ZnS particles. The visible luminescent radiation at 590.1 nm is due to Mn impurities. The dominant emission band at short wavelengths exhibits a quadruple fine structure with peaks located at 416.1, 423.9, 430.1, and 437.8 nm which are identified with optical transitions arising from vacancy and interstitial sites for both Zn and S atoms. © 1998 American Institute of Physics.
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82.70.Dd Colloids
61.46.-w Structure of nanoscale materials
78.55.Et II-VI semiconductors
71.20.Nr Semiconductor compounds
72.80.Ey III-V and II-VI semiconductors

Optical studies of GaInP(ordered)/GaAs and GaInP(ordered)/GaP/GaAs heterostructures

S. H. Kwok, P. Y. Yu, J. Zeman, S. Jullian, G. Martinez, and K. Uchida

J. Appl. Phys. 84, 2846 (1998); http://dx.doi.org/10.1063/1.368426 (9 pages) | Cited 4 times

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We report on a detailed optical study of emission from a series of GaInP (ordered)/GaAs heterostructures. Some of these structures contain one or two thin ( ∼ 2 nm) layers of GaP between the GaInP and GaAs layers. A so-called “deep emission” band at 1.46 eV is observed in all our samples. However, at high excitation power, an emission above the band gap of GaAs (previously identified as quantum well emission) emerges only in structures where GaP layers are inserted on both sides in between the GaAs well and its GaInP barriers. From the pressure dependence we have identified the deep emission peak as due to donor–acceptor pair transitions at the GaAs/GaInP interface. The insertion of GaP layers between the GaInP (ordered) and GaAs layers helps to suppress the defects which contribute to this deep emission. By applying pressure to the sample which exhibits quantum well emission we have determined its band alignments. We show that the GaP layers form two effective barriers for confining electrons within the GaAs well. However, the magnetic field dependence of the quantum well emission reveals that the electrons form only a quasi-two-dimensional gas inside the GaAs well. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Ls Magneto-optical effects

The electronic structure and optical properties of intermixed GaAs/AlGaAs double quantum wells

Maolong Ke, A. Saher Helmy, A. C. Bryce, J. H. Marsh, J. Davidson, and P. Dawson

J. Appl. Phys. 84, 2855 (1998); http://dx.doi.org/10.1063/1.368444 (3 pages)

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We report photoluminescence and photoluminescence excitation (PLE) investigations of intermixed GaAs/AlGaAs double quantum wells. The PLE spectra provide energy information about many different transitions, from which the band profile can be more reliably derived. Using the widely assumed error function profile, it was not possible to explain the observed results. Detailed analysis revealed that the as-grown sample had a graded interface which affected the band profile for the intermixed samples. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Dielectric tensor formulation of magnetic dichroism sum rules

Dai Zhao, Hartmut Höchst, and David L. Huber

J. Appl. Phys. 84, 2858 (1998); http://dx.doi.org/10.1063/1.368427 (3 pages) | Cited 1 time

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A formalism is developed to interpret the magnetic circular dichroism (MCD) sum rules in terms of the complex dielectric tensor ϵ(ω). Utilizing classical Maxwell–Fresnel theory, the formalism is applied to the reflection spectra of Fe at the M2,3 transition to calculate the orbital moments 〈Lz〉. The analysis shows that due to the energy dependence of the unpolarized normalization integral and the absence of a well-defined cut-off energy across the transition edge, large errors can be introduced. Uncertainties in 〈Lz〉 by more than 100% are possible which makes a comparison with other literature values questionable. Due to the arbitrary energy cut-off, the application of the sum rules as a general tool to unambiguously decompose MCD spectra into orbital and spin components should be practiced with great caution. © 1998 American Institute of Physics.
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78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.50.Bb Fe and its alloys

Optical characterization of AlN films grown by plasma source molecular beam epitaxy

Regina Y. Krupitskaya and Gregory W. Auner

J. Appl. Phys. 84, 2861 (1998); http://dx.doi.org/10.1063/1.368428 (5 pages) | Cited 21 times

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Thin films of AlN were grown on Si(111), sapphire (1102), and sapphire (0001) substrates by plasma source molecular beam epitaxy (PSMBE). Optical transmission spectra of PSMBE grown AlN/sapphire show neither significant band edge distortions nor deep level absorption in the spectral range 0.2–6.5 μm. Furthermore, there is no evidence of deep levels in the spectra of AlN/Si in the range 2.5–25 μm. The optical phonon modes of AlN/Si films were directly observed in infrared transmission and 80° angle of incidence reflectance spectra. Longitudinal optical (900 cm−1) and transverse optical (680 cm−1) modes are shifted toward each other comparable to previously reported bulk values. Optical spectra of thick textured film samples with low degree of orientation have phonon energies close to bulk values (probably due to strain relaxation). © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Fs III-V and II-VI semiconductors

The structural and optical properties of high quality ZnTe grown on GaAs using ZnSe/ZnTe strained superlattices buffer layer

R. C. Tu, Y. K. Su, H. J. Chen, Y. S. Huang, S. T. Chou, W. H. Lan, and S. L. Tu

J. Appl. Phys. 84, 2866 (1998); http://dx.doi.org/10.1063/1.368429 (5 pages) | Cited 2 times

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This work studied the structural and optical properties of ZnTe epilayers grown on GaAs substrates with ZnSe/ZnTe strained superlattices buffer layers. Material properties were characterized using cross-sectional transmission electron microscopy, photoluminescence (PL), contactless electroreflectance (CER), and piezoreflectance (PzR). PL spectra clearly distinguished the strong free exciton peaks, weak donor-acceptor pair, Y lines, and oxygen-bound exciton peaks, indicating the high quality of the films. In addition, the CER and PzR spectra were compared to ascertain that ZnTe epilayers of 1.5 μm in thickness grown on GaAs substrates are under a biaxial tensile strain. An attempt was also made to identify the origins of the near-band-edge transitions of ZnTe epilayer in the CER and PzR spectra by comparing these spectra with PL spectra and the second harmonic frequency CER. By doing so, the interference below the band gap of ZnTe could be effectively eliminated. Moreover, the energy splitting between heavy- and light-hole valence bands at 15 K was calculated by utilizing the temperature-dependent elastic constants for ZnTe and the thermal-expansion coefficients for ZnTe and GaAs. The discrepancy between experiment and calculation indicates that the residual mismatch-induced strain and the thermally induced strain in ZnTe epilayers grown on GaAs during cooling must be simultaneously considered. © 1998 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.20.Jq Electro-optical effects
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.55.Gs II-VI semiconductors
62.20.D- Elasticity
65.40.De Thermal expansion; thermomechanical effects

Photoelectron spectroscopy of chalcopyrites and Zn based II–VI semiconductor heterostructures

M. Wörz, E. Pschorr-Schoberer, R. Flierl, H. Preis, and W. Gebhardt

J. Appl. Phys. 84, 2871 (1998); http://dx.doi.org/10.1063/1.368430 (5 pages) | Cited 3 times

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We have investigated CuInSe2 surfaces as well as the interfaces of the systems ZnSe/CuInSe2 and ZnS/CuInSe2 by vacuum ultraviolet photoelectron spectroscopy with synchrotron radiation. The CuInSe2 substrates are prepared with a hydrogen plasma and show high quality surfaces suitable for further growth of ZnSe in order to determine the valence-band offset of ZnSe/CuInSe2. At the surface of CuInSe2 Se atoms have been replaced by Te or S atoms, so that CuInTe2 or CuInS2 surfaces were formed. We determined the valence-band offsets of CuInTe2/CuInSe2 and CuInS2/CuInSe2 to be ΔEvb(CuInTe2/CuInSe2) = (0.85±0.05)eV and ΔEvb(CuInS2/CuInSe2) = (0.87±0.05)eV. ΔEvb(ZnSe/CuInSe2) = −(0.5±0.1)eV is in good agreement with values from literature. Furthermore we have examined the interface ZnS/CuInS2 and obtained the valence-band offset ΔEvb(ZnS/CuInS2) = −(2.3±0.1)eV. © 1998 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states

A photoelectron spectroscopy study of Ti/Cu interfaces

J. Geng, A. Schüler, P. Reinke, and P. Oelhafen

J. Appl. Phys. 84, 2876 (1998); http://dx.doi.org/10.1063/1.368431 (6 pages) | Cited 3 times

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Reactions at Ti/Cu interfaces were investigated by ultraviolet and x-ray photoelectron spectroscopy (UPS, XPS). For Ti deposition onto copper substrates at ambient temperature, our measurements strongly suggest that at the interface an amorphous alloy is formed. This idea is supported by the comparison of our UPS data to the ones of bulk glassy CuxTi1−x. The thickness of this amorphous interlayer which is built up onto the polycrystalline Cu substrate corresponds to a nominal Ti coverage of about 10 monolayers. At a substrate temperature of 300 °C, however, the interface reaction is still present at nominal Ti coverages over a hundred monolayers. Presumably the crystalline phase Cu3Ti2 is formed. © 1998 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Fx Diffusion; interface formation

Effects of post-growth treatment and coating with ultrathin metal layers on the band bending and field electron emission of diamond films

V. I. Polyakov, N. M. Rossukanyi, A. I. Rukovishnikov, S. M. Pimenov, A. V. Karabutov, and V. I. Konov

J. Appl. Phys. 84, 2882 (1998); http://dx.doi.org/10.1063/1.368394 (8 pages) | Cited 40 times

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Band bending formation on thin nanocrystalline diamond films and field electron emission after post-growth treatments was investigated. It was found that treatment of the diamond surface with hydrogen plasma substantially decreases the density of point defects, forms the downward band bending and enhances the field electron emission from the films. In the case of an argon plasma treated diamond surface, new point defects were induced and their energy distribution was changed. Nevertheless, the downward band bending was formed and the field electron emission was enhanced similar to the H–plasma-treated diamond surface with minor density of defects. These effects were interpreted in terms of the electrical dipole formation on the plasma treated diamond surfaces. Coating the diamond films with ultrathin metal (Ni, Ti) layers revealed the dependence of the band bending and field emission behavior on the type and thickness of the metal used. The deposition of a few monolayers of Ni on the diamond surface was found to raise the position of the Fermi level relative to the valence band maximum and cause the downward band bending, reducing the field emission threshold. It was suggested that the charge of the surface dipoles on the metal coated diamond surfaces (as in the case of the H and Ar plasma treatments) plays a key role in the band bending formation. © 1998 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.65.-b Surface treatments
73.20.At Surface states, band structure, electron density of states
81.05.ub Fullerenes and related materials
61.72.J- Point defects and defect clusters

Escape length of ultraviolet induced photoelectrons in alkali iodide and CsBr evaporated films: Measurements and modeling

T. Boutboul, A. Akkerman, A. Breskin, and R. Chechik

J. Appl. Phys. 84, 2890 (1998); http://dx.doi.org/10.1063/1.368395 (7 pages) | Cited 10 times

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The escape length of electrons photoinduced from thin CsI, KI, RbI, NaI, and CsBr evaporated films was measured in the 140–180 nm photon spectral range. Theoretical model predictions of the escape length value are in fair agreement with the experimental results. They vary between 10 and 40 nm, the highest values being for CsI, RbI and CsBr. For CsI, measured and calculated ultraviolet-induced escape length values are consistent with that determined from x-ray photoemission quantum yield data. Post-evaporation annealing of the films had no major impact on the measured electron transport properties. © 1998 American Institute of Physics.
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73.61.Ng Insulators
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