Lina Gunawan

Structural relaxation of acetaminophen glass.

PurposeThe aim is to determine the structural stability of acetaminophen glass with time and temperature change, and to examine the merits of adapting the structural relaxation models of the glassy state for pharmaceuticals.MethodsDifferential scanning calorimetry technique has been used to study the acetaminophen glass after keeping the samples for various periods at fixed temperatures and after keeping at various temperatures for fixed periods.ResultsA general formalism for thermodynamic changes during storage in a temperature fluctuating environment is given and the kinetics of the enthalpy and entropy decrease determined. At a fixed temperature, the decrease occurs according to a non-exponential kinetics. For the same storage time, but at different temperatures, the enthalpy and entropy decrease rises to a maximum value at a certain temperature and then declines. The peak appears at the temperature at which the internally equilibrated state of the sample is reached for a fixed storage time. The change in the normalized heat capacity during the heating of acetaminophen has been analysed in terms of a non-exponential, non-linear enthalpy relaxation model.ConclusionA single set of parameters that fit the data for unannealed acetaminophen glass does not fit the calorimetric data for annealed glass. Since acetaminophen molecules form intermolecular hydrogen-bonds in the crystal state and likely to form such bonds more easily in the disordered state, effect of such bonds on structural relaxation is likely to be significant.

Epitaxial thin films of multiferroic Bi2FeCrO6 with B-site cationic order

Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed X-ray diffraction and cross-section transmission electron microscopy analysis revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+ cation ordering along the [111] direction. The films contain no detectable magnetic iron oxide impurities and have the correct cationic average stoichiometry throughout their thickness. They however exhibit a slight modulation in the Fe and Cr compositions forming complementary stripe patterns, suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO films exhibit good ferroelectric and piezoelectric properties, in addition to magnetic properties at room temperature, as well as an unexpected crystallographic orientation dependence of their room temperature magnetic properties. Our results qualitatively confirm the predictions made using the ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along with the unpredicted existence of magnetic ordering at room temperature.

Imaging, Core-Loss, and Low-Loss Electron-Energy-Loss Spectroscopy Mapping in Aberration-Corrected STEM

High-angle annular dark-field and annular bright-field imaging experiments were carried out on an aberration-corrected transmission electron microscope. These techniques have been demonstrated on thin films of complex oxides Ba3.25La0.75Ti3O12 and on LaB6. The results show good agreement between theory and experiments, and for the case of LaB6 they demonstrate the detection of contrast from the B atoms in the annular bright-field images. Elemental mapping with electron-energy-loss spectroscopy has been used to deduce the distribution of Cr and Fe in a thin film of the complex oxide Bi2(Fe1/2Cr3/2)O6 at the unit cell level and the changes in the near-edge structure within the inequivalent regions in the crystalline unit cell. Energy-filtered images in the low-loss region of the energy-loss spectrum show contrast and resolution consistent with the modulation of the signals from elastic scattering. High-resolution contrast, mediated by phonon scattering, is observed for interband transitions. The limitations in terms of detection and signal are discussed.

Structural and multiferroic properties of epitaxial γ-Fe 2 O 3 -BiFeO 3 /Bi 3.25 La 0.75 Ti 3 O 12 composite bi-layers

Multiferroic properties of γ -Fe2O3–BiFeO3/Bi3.25La0.75Ti3O12 epitaxial composite bi-layers grown on SrRuO3/SrTiO3(1 1 1) are compared with the properties of single phase BiFeO3 and Bi3.25La0.75Ti3O12 thin films. The composite bi-layers show well-saturated hysteresis loops with a low coercive field, a high fatigue resistance and high saturation magnetization. The insulating Bi3.25La0.75Ti3O12 underlayer reduces significantly both the leakage current and the coercive field of the heterostructure (200 kV cm −1 ) at the expense of a lower polarization (20 µ Cc m −2 ), while the epitaxial γ -Fe2O3 secondary phase that develops within the relaxed epitaxial BiFeO3 matrix allowed for a high saturation magnetization. (Some figures in this article are in colour only in the electronic version)

Locating La atoms in epitaxial Bi3.25La0.75Ti3O12 films through atomic resolution electron energy loss spectroscopy mapping

Atomic resolution high-angle annular dark-field imaging of La-doped bismuth titanate (BLT), Bi3.25La0.75Ti3O12, has been carried out with an aberration-corrected transmission electron microscope. The HAADF image revealed the presence of defects in the [Bi2O2]2+ layers and extra atomic rows between the [Bi2O2]2+ layers and the [Bi2Ti3O10]2− perovskite slabs. Electron energy loss spectroscopy elemental mapping at atomic resolution revealed the exact location of La dopants in the bismuth titanate parent unit cell. These results are discussed in terms of large remanent polarization and enhanced fatigue resistance in BLT.

Growth, Structure and Properties of BiFeO 3 -BiCrO 3 Films obtained by dual cross beam PLD

Bi2FexCryO6 epitaxial films have been grown on (100)-and (111)-oriented SrTiO3 substrates using dual crossed beam pulsed laser deposition (DCB-PLD). The films crystal structure, chemical composition ferroelectric and magnetic properties were investigated and are reported.

Microstructure and ferroic properties of epitaxial [γ-Fe2O3–BiFeO3]−Bi3.25La0.75Ti3O12 composite bilayers

Epitaxial [γ-Fe2O3–BiFeO3]/Bi3.25La0.75Ti3O12 and Bi3.25La0.75Ti3O12/[γ-Fe2O3–BiFeO3] composite bilayers were grown on SrRuO3 coated (111) SrTiO3 substrates in order to investigate the influence of the morphology of the γ-Fe2O3–BiFeO3 self assembled nanocomposite layer on the multiferroic properties of the bilayer. Both types of bilayers exhibit high resistivity and simultaneously ferroelectricity and ferrimagnetism at room temperature. When the γ-Fe2O3–BiFeO3 composite layer is sandwiched between the Bi3.25La0.75Ti3O12 film and the substrate, the BiFeO3 component is not only subjected to epitaxial strain induced by the surface on top of which it grows but also to elastic interactions with the Bi3.25La0.75Ti3O12 capping layer. The latter indeed reduce the amount of γ-Fe2O3 inclusions, affects the morphology of the grains in the γ-Fe2O3–BiFeO3 layer, and increases the shape anisotropy of the γ-Fe2O3 inclusions. Additionally, this modification in the microstructure of the γ-Fe2O3–BiFeO3 layer induces an imp...

Growth, structure, and properties of BiFeO/sub 3/-BiCrO/sub 3/ films obtained by dual cross beam PLD

Bi₂Fe_xCr_yO₆ epitaxial films have been grown on (100)-and (111)-oriented SrTiO₃ substrates using dual crossed beam pulsed laser deposition (DCB-PLD). The films crystal structure, chemical composition ferroelectric and magnetic properties were investigated and are reported.

Structural investigation of interface and defects in epitaxial Bi3.25La0.75Ti3O12 film on SrRuO3/SrTiO3 (111) and (100)

The structure of La-doped bismuth titanate (BLT), Bi3.25La0.75Ti3O12, is investigated with atomic resolution high-angle annular dark field (HAADF) scanning transmission electron microscopy. The images reveal evidence of the tilting of TiO6 octahedra within the perovskite-like layers of the BLT unit cell. The tendency of La ions to substitute Bi ions and occupy the top part of the (Bi2O2)2+ layer, previously observed from electron energy loss spectroscopy (EELS) mapping experiments, is explained based on the tolerance factors and stress relief mechanism. The atomic resolution HAADF images also reveal the presence of the out-of-phase boundaries (OPBs). The role of OPBs in BLT is discussed in terms of its fatigue resistance as the OPBs provide extra nucleation sites for ferroelectric domains during polarization reversals. Further, we show evidence that the first deposited atomic layer at the interface also governs the subsequent film growth, resulting in the modulation of the “defect-free” and the “defected”...

High-accuracy electron tomography of semiconductor devices

As semiconductor industries have implemented three dimensional (3-D) structures in order to improve device performance, i.e., to decrease power requirement and to lower current leakage, a conventional 2D TEM cross-section is no longer sufficient to visualize the structure of a device. Electron Tomography (ET) provides more comprehensive representation in comparison to conventional 2-D cross section TEM images. Electron tomography allows for object visualization of practical interest at sub-nm resolution in 3D. For undistorted rendering and accurate measurement of object dimensions the data must be acquired over the entire ±90° tilt range and the accuracy of the alignment of the projected images must be better than the desired resolution of the reconstructed volume [1]. Here we discuss high resolution ET investigation of semiconductor devices using nano-dot fiducial markers on samples without a missing wedge.