Joo Tien Oh

LiTaO3 films with c-axis preferred orientation prepared on Si(111) substrate by sol-gel method

LiTaO3 films with c-axis preferred orientation have been prepared on Si(111) substrates using sol–gel spin-coating and rapid thermal annealing. Hydrogen-terminated silicon surface, preheating temperature, and unidirectional heat flow during the heat treatment are essential factors for the c-axis texture. The texture is useful in pyroelectric, metal-ferroelectric-semiconductor (MFS) nonvolatile memory, and integrated optics applications.

F spots and domain patterns in rhombohedral PbZr0.90Ti0.10O3

The microstructure of PbZr0.9Ti0.1O3 ceramics is studied by transmission electron microscopy. Two types of domain patterns are found, namely, the 109° domain with the F spots (12{hkl} superlattice reflections) observed in neighboring domains and the 71° domain with the F spots observed in one domain and having disappeared in the neighboring one. The computer simulation indicates that the F spots are forbidden at h=k positions so that they do not appear in the electron diffraction pattern if viewed along the [110] direction. Based on this result, the observed two types of domain patterns and their corresponding diffraction patterns can be explained.

The formation of micrometer-long TiO2 nanotube arrays by anodization of titanium film on conducting glass substrate

Micrometer-long titanium oxide nanotube arrays, tens of nanometers in diameter, were fabricated by anodization of titanium film coated on a conducting glass substrate. The Ti film was deposited by magnetron sputtering at room temperature. The effect of anodizing conditions on the formation of TiO2 nanotubes was investigated. The results indicate that dense and uniform Ti film deposited under 150 W at room temperature was favorable for the formation of ordered nanotube arrays. The average diameter of the TiO2 nanotubes varied from 35 to 95 nm when the anodization potential changed from 10 to 40 V. Micrometer-long nanotubes (1.1 μm) with good adhesion to the substrate could be obtained in 0.5 wt% NH4F/glycerol at 30 V for 2 h. After heat treatment, the crystalline anatase nanotubes show enhanced photoelectrochemical activity compared with those anodized in 1 M H3PO4/0.5 wt% HF. This is attributed to the increased light-harvesting abilities.

Effect of A-Site Substitution of Calcium on Zr-Rich Lead Zirconate Titanate

Effect of calcium substitution on the A-site of Zr-rich lead zirconate titanate Pb(Zr 0.94 Ti 0.06 )O 3 and Pb(Zr 0.92 Ti 0.08 )O 3 is studied. It is found that the rhombohedral structure of Zr-rich lead zirconate titanate changes to tetragonal and finally to cubic with increasing amount of calcium substitution. Both the dielectric constant and the Curie temperature decrease with the substitution of calcium on the A-site of the ABO 3 perovskite structure. A pyroelectric current peak is observed which is resulted from the phase transition from the low temperature rhombohedral ferroelectric phase F R ( LT ) to the high temperature F R ( HT ) one. Small amount of calcium substitution increases the peak value and also shifts the peak position to higher temperatures. However, further increase in the calcium content lowers the peak value and finally smears out the peak.

Stress Effect on the Pyroelectric Properties of Lead Titanate Thin Films

In the application of thin ferroelectric films to IR sensors, problems may arise to affect the sensitivities of the devices. The effects to influence the pyroelectric properties can be mainly categorized into two groups. One is the intrinsic effect due to the reduction in grain size. The other is the effect caused by residual stress. In this paper the stress effect on the pyroelectric properties of PbTiO 3 thin films will be studied by using the Landau-Ginsburg-Devonshire (LGD) phenomenological theory. It is found that a compressive stress increases the figure of merit while a tensile stress increases the pyroelectric coefficient for the films with the polarization vectors normal to the surface.

The ferroelectric–antiferroelectric transition in Pb[Zr0.9(CexTi1−x)0.1]O3 due to Ce4+ doping

The effect of B-site substitution of Ce4+ on the microstructure of the Pb[Zr0.9(CexTi1−x)0.1]O3 (0≤x≤0.7) ceramics is studied by transmission electron microscopy (TEM). For x=0, only 12{hkl} superlattice reflections are found in the selected area diffraction patterns (SADPs), which correspond to the anti-phase rotation of the oxygen octahedra. Small amount of Ce4+ substitution causes the in-phase tilting of the oxygen octahedra and results in the 12{hk0} superlattice reflections. With 7 mol% addition of Ce4+ on the B-site, the superlattice reflections at the 14{hk0} pseudocubic positions can be observed, indicative of the existence of the antiferroelectric (AFE) phase. The result conforms to the polarization–electric field (P–E) hysteresis loop measurements on the corresponding bulk ceramic samples.

Stress- and strain-relaxation in lead zirconate titanate based ceramics

The stress- and strain-relaxation behavior of lead zirconate titanate based ceramics is studied by using the three-point bending test. The relaxation behavior has been explained based on the domain reorientation mechanism. It is found that the stress relaxation behavior obeys a logarithmic time law. It has also been experimentally confirmed that above the Curie temperature where all the domains disappear, there is no relaxation in the ferroelectric ceramics.

The effect of milling speed on the magnetic properties of mechanically alloyed Fe-45%Ni powders

FeNi-based alloys are commonly used as soft magnetic materials, exhibiting high permeability, low coercivity and high saturation magnetization. The present study is focused on the effect of the milling speed (vial and disc rotation speed) on the magnetic properties of nanocrystalline Fe-45 wt. % Ni powders. The phase analysis and the structural properties were characterized by the use of X-ray diffraction. Structural parameters including lattice parameter, crystalline size and lattice strain were obtained from Rietvelds powder structure refinement analysis of X-ray powder diffraction data. The magnetic measurements were performed, using a vibration sample magnetometer (VSM) at room temperature. The results showed that the higher milling speed leads to larger lattice parameter, lower crystalline size, higher saturation magnetization and lower coercivity of the investigated system.

Evaluation of thin film by chemical vapor deposition using x-ray diffraction

X-ray diffraction techniques are increasingly being used for the evaluation of thin film in the microelectronics industries. The techniques use low angle scanning with an X- ray diffractometer. It is capable of determining the structure of the thin film material and its thickness on the substrate. X-ray diffraction techniques on thin film has the advantage over transmission electron microscopy that requires elaborate sample preparation which is time consuming, difficult and artefacts are often introduced during ion milling. In X-ray diffraction, the coated sample can be used without preparation. This paper discusses some recent advances in X- ray diffraction of thin films using parallel incident beam with a wide angle goniometer and a thin film attachment. It also discusses the results obtained on four materials coated with a thin film by chemical vapor deposition.