Wai-Hung Chan

Ion-beam-induced surface damages on tris-(8-hydroxyquinoline) aluminum

Surface damage of tris-(8-hydroxyquinoline) aluminum (Alq3) film by 100 eV Ar+ irradiation has been studied by using both x-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). XPS core level electron density curves revealed that some N–Al and C–O–Al bonds in Alq3 molecules were broken by the irradiation. Correspondingly, the valence band structure of the Alq3 molecule, as measured by UPS, was tremendously changed. The highest occupied state extended towards the Fermi level (EF), implying that a metal-like conducting surface was formed. This kind of damaged surface would cause nonradiative quenching in an electroluminescence device when electrons are injected from the cathode into the Alq3 layer, and possibly result in electrical shorts.

Phase transformation and electric field tunable pyroelectric behavior of Pb(Nb,Zr,Sn,Ti)O3 and (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric thin films

Phase transformation and pyroelectric behavior of Pb(Nb,Zr,Sn,Ti)O3 (PNZST) and (Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectric (AFE) thin films were investigated as a function of temperature and dc bias field. A large pyroelectric coefficient of the order of ∼3×10−7Ccm−2K−1 was realized at the ferroelectric (FE) to AFE and the AFE to FE phase transformations in the PLZST and PNZST films, respectively. The phase transformation temperature could be readily adjusted by dc bias for both films. The large pyroelectric coefficient combined with excellent dc tunability at the phase transformation temperature makes these two systems promising candidates for uncooled tunable pyroelectric thermal sensing applications.

Effect of La substitution on phase transitions in lead zirconate stannate titanate (55/35/10) ceramics

Investigations of the structure-property relationships in Pb1−3x∕2Lax(Zr0.55Sn0.35Ti0.10)O3. (PLZST100x∕55∕35∕10) have been performed for x between 0 and 0.08 by means of x-ray diffraction, electron microscopy, polarization, and dielectric studies. Factors affecting the phase stability were determined. The base composition PLZST0∕55∕35∕10 was ferroelectric (FE) at room temperature and transformed into an incommensurate antiferroelectric (AFEin) state on heating. Evidence was presented that low La addition could destabilize the FE state and PLZST2∕55∕35∕10 became AFEin at room temperature, which transformed to a multicell cubic state and then to a paraelectric (PE) phase upon heating. Further increase of La content enhanced the stability of the AFEin state at room temperature. Moreover, addition of La could also broaden the AFEin-PE phase transition temperature region and decrease its maximal dielectric constant emax′.

Uncooled tunable pyroelectric response of antiferroelectric Pb0.97La0.02(Zr0.65Sn0.22Ti0.13)O3 perovskite

Pb0.97La0.02(Zr0.65Sn0.22Ti0.13)O3 ceramic was confirmed to be in an antiferroelectric (AFE) phase at T<170°C by macroscopic and microscopic studies. The electric-field-induced ferroelectric (FE) state was found to exhibit a much longer lifetime than the reasonable laboratory measuring time scale at T<60°C, which has led to the frequent misinterpretation of this material system as FE. The dc bias dependence of the dielectric and pyroelectric properties was studied as a function of temperature. The poled sample exhibited a low dissipation factor (tanδ∼0.03), a large transient pyroelectric coefficient of the order of 10−3–10−2Cm−2K−1, and excellent dc tunability at the FE-to-AFE transition temperature (39°C∕kV∕mm). The possible application of this material to uncooled tunable pyroelectric thermal sensing is also discussed.

Microstructural evolution and macroscopic property relationship in antiferroelectric lead lanthanum stannate zirconate titanate ceramics

The antiferroelectric (AFE) Pb0.97La0.02(Zr0.60Sn0.30Ti0.10)O3 ceramic has a composition near the morphotropic phase boundary that separates the AFE from the ferroelectric (FE) phase. Its structural changes as well as macroscopic properties were investigated over a temperature range of −180–300 °C using transmission electron microscopy, dielectric spectroscopy, and Sawyer–Tower polarization measurements. The previously reported tetragonal AFE phase is shown to be an incommensurate orthorhombic phase and it exhibits a sequence of phase transformations on heating from the incommensurate AFE to a multicell cubic, then to a simple cubic phase. This microstructural evolution with temperature is consistent with the corresponding macroscopic dielectric and AFE behaviors. The temperature dependence of the AFE-FE switching field is closely associated with the corresponding temperature dependence of the incommensurate modulation wavelength.

Deposition of ultra-thin diamond-like carbon protective coating on magnetic disks by electron cyclotron resonance plasma technique

Abstract Diamond-like carbon (DLC) films were prepared on Si and magnetic disks using an electron cyclotron resonance assisted microwave plasma chemical vapour deposition system with variable radio-frequency (rf) substrate bias. Surface morphology of disks deposited with 10 nm DLC was observed under atomic force microscopy (AFM), which revealed surfaces smoother than the uncoated disk. The root-mean-square roughness decreased with increasing substrate bias and reduced to 0.23 nm for film prepared at a bias of −150 V. Internal stress and hardness of the resulting films deposited on Si were investigated by curvature measurement and nano-indentation, respectively. Both internal stress and hardness increased with increasing ion energies. At a bias beyond −120 V, the film structure changed from diamond-like to graphite-like. There was also an improvement of scratch resistance of the DLC coatings deposited at bias >−90 V.

Temporal effect of low-temperature ferroelectric behaviors in Pb0.97La0.02(Zr0.60Sn0.30Ti0.10)O3 ceramics

Kinetic behaviors of unusual low-temperature ferroelectric properties of Pb0.97La0.02(Zr0.60Sn0.30Ti0.10)O3 ceramic were studied. In a wide temperature range it reveals the antiferroelectric properties with pronounced polarization versus electrical field hysteresis double loops resulting from the field-induced antiferroelectric-to-ferroelectric switching. The reverse switching time is temperature dependent, and below 210 K this time overcomes the reasonable laboratory time scale. Kinetic data were analyzed to yield the activation energy. At as low as 100 K all experimental results suggest that the ground state of the system remains antiferroelectric, thus the time-dependent dielectric properties owe their origin to the kinetic effects.

Temporal Effects in Dielectric Properties of Some Antiferroelectric Complex Perovskites

Two complex perovskite antiferroelectric (AFE) systems were studied; they are Pb0.97La0.02(Zr0.6Sn0.3Ti0.1)O3 (PLZST) in ceramic form and Pb0.99Nb0.02(Zr0.82Sn0.12Ti0.04)0.98O3 (PNZST) in thin film form. Dielectric and transmission electron microscopy (TEM) studies of the PLZST ceramics confirmed the AFE nature of the specimen, but at low temperature the electrical field application could induce a temporary ferroelectric (FE) phase with characteristic life‐time dependent on temperature This life‐time reaches a value of ∼ 0.1s at 248K. Further decrease of temperature leads to a much faster than Arrhenius growth of the recovery time, which eventually exceeds the reasonable laboratory time scale below 210K. We believe that the strongly temperature‐dependent kinetics arises from a cooperative freezing of the incommensurate AFE order in the presence of quenched composition disorder. The PNZST films’ polarization properties are highly dependent on the film thickness and at the lowest studied limit (∼170 nm) the...