Functional Oxides with Nitride Buffer Layers for Heteroepitaxial Devices

As conventional memory technologies approach their limit of scalability, there is a quest to find new technologies to replace existing memories. Of the emerging switching phenomena, ferroelectric switching and resistive switching have been considered for this work. Ferroelectricity is a property by which a material develops a spontaneous polarization that can be reversed by and external electric field. Resistive switching, the basis for the novel “memristor” devices, is a property that enables a device switch to a low or high resistance state depending on the magnitude and polarity of the applied voltage. In this work, various nanostructures have been explored to achieve property enhancement in functional oxides. For example, vertically aligned nanocomposite structures consist of two different materials that are simultaneously deposited onto a single substrate, and grow as two distinct phases. Vertically aligned nanocomposite structures offer the advantage of strain tuning through the vertical interfaces between phases. First, to improve the ferroelectric properties of BaTiO3, a conventional ferroelectric material, epitaxial vertically aligned nanocomposite BaTiO3-CeO2 films have been deposited on SrTiO3 substrates. These films exhibit a columnar structure with high epitaxial quality. The films show a similar ferroelectric response as that of pure thin film BaTiO3, but with an improved Curie temperature, despite the incorporation of CeO2. These nanocomposite structures have been replicated on Si substrates using a double buffer layer of SrTiO3/TiN to achieve the eventual integration of these films on Si. No reduction in ferroelectric properties has been observed, but the films again showed an improvement in the Curie temperature. Second, a simple resistive switching device has been demonstrated by the in situ partial oxidation of a TiN film under three different oxidation time periods. The oxidized region consists of near stoichiometric TiO2, and serves as the oxide layer, while the unoxidized TiN serves as the bottom electrode. All films exhibit bipolar resistive switching and all films are forming-free. The forming-free property is attributed to an oxygen deficient TiO2-x layer at the interface between the oxide and nitride regions. Third, ZnO, a piezoelectric, has been selected as another complementary second phase material for BaTiO3. Epitaxial and highly textured vertically aligned BaTiO3-ZnO composite films have been deposited on SrTiO3 substrates and SrTiO3/TiN buffered Si substrates, respectively. Electrical characterization shows that the films grown on both substrates are ferroelectric at room temperature and exhibit similar properties. Composition analysis shows that both the laser fluence and the oxygen partial pressure can modulate the Ba/Ti cation stoichiometry which, in turn, impacts the ferroelectric properties. This is the first demonstration of the vertically aligned nanocomposite of BaTiO3 and ZnO and its silicon based integration. Finally, based on the excellent buffer layer and diffusion barrier properties of TiN for integrating functional oxides on Si, TiN has been applied as a protective layer on metal surfaces. A 500 nm thick TiN layer has been demonstrated to serve as an excellent diffusion barrier in extreme environments

Improving Fluorescence Lifetime Imaging Microscopy Deconvolution Using Constrained Laguerre Basis Functions

Fluorescence lifetime imaging microscopy (FLIM) is a noninvasive invasive optical imaging modality which is finding new applications in medical imaging. In FLIM, the fluorescence time decay is measured at a pixel. The fluorescence impulse response function (IRF) is then estimated using a deconvolution of the instrument response and the measured fluorescence time decay. Two of the challenges facing FLIM are speed of the deconvolution and the accuracy of the IRFs. The linear expansion of the fluorescence decays based on the orthonormal Laguerre basis functions (LBFs) is among the fastest methods for estimating the IRFs. The automated implementation to optimize the Laguerre parameter improves the speed of the deconvolution using the LBFs but uses a global optimization. Therefore, the IRFs do not necessarily mimic exponential time decays, or monotonically decreasing functions. On the other hand, applying a constraint to the LBFs using the Active Set Nonnegative Least Squares (NNLS) method improves the IRF estimation. The estimation of the Laguerre parameter using the NNLS method, however, is about 10-15x slower. By combining these two deconvolution techniques, we found that the deconvolution time is similar to the automated global Laguerre parameter deconvolution while the IRF estimation always results in a monotonically decreasing function

“Omics” Signatures in Peripheral Monocytes from Women with Low BMD Condition

Postmenopausal osteoporosis (PMO) is a result of increased bone resorption compared to formation. Osteoclasts are responsible for bone resorption, which are derived from circulating monocytes that undertake a journey from the blood to the bone for the process of osteoclastogenesis. In recent times, the use of high throughput technologies to explore monocytes from women with low versus high bone density has led to the identification of candidate molecules that may be deregulated in PMO. This review provides a list of molecules in monocytes relevant to bone density which have been identified by “omics” studies in the last decade or so. The molecules in monocytes that are deregulated in low BMD condition may contribute to processes such as monocyte survival, migration/chemotaxis, adhesion, transendothelial migration, and differentiation into the osteoclast lineage. Each of these processes may be crucial to the overall route of osteoclastogenesis and an increase in any/all of these processes can lead to increased bone resorption and subsequently low bone density. Whether these molecules are indeed the cause or effect is an arena currently unexplored

Ramifications of varying banking regulations on performance of Islamic Banks

Recent financial crises have highlighted the importance of banking regulations to hedge against the high risk accredited to imbalances in banks' balance sheets. Nonetheless, banking regulations may have adverse effects. On the one hand, they serve as prudential measures that alleviate the effects of crises on the stability of the banking system while on the other hand; they may increase the cost of intermediation and reduce banks' profitability. Implementation of non-suitable regulations such as Islamic banks adopting conventional banks regulations could also impair banks' performance. This paper analyses the linkages between bank regulatory and supervisory structures associated with Basel III's pillars has any significant impact on Islamic banks' performance in Asia and Gulf Cooperation Council (GCC) using two-step Generalized Methods of Moments (GMM) technique. Findings suggest that regulatory variables are positively significant with Islamic banks' performance in Asian region but not in the GCC

Islamic legal methodologies and Shariah screening standards: application in the Indonesian stock market

This article provides a framework for applying the principles of Islamic legal methodology to determine the optimal Shariah screening standards for Islamic equity markets. It is argued that using maslahah mursalah (unrestricted benefit) is an appropriate method for identifying appropriate financial standards and its principles stipulate that the benchmark that yields the best economic returns to investors should be chosen. The methodological framework is applied to the Indonesia equity market where the economic implications of the Islamic stock screening standards of the Indonesian Islamic Shariah Stock Index and four global indices are assessed. Portfolios are constructed by applying Islamic stock screening standards for each of the indices by using data on 377 stocks listed in the Indonesian stock market for 5 years. The performances measured by the Sharpe ratio, Treynor index, and Jensen alpha reveal that the Dow Jones Islamic Index screening criteria performs the best. Based on the method of maslahah mursalah, the article recommends using the screening standard of this index in the Indonesian stock market to maximize benefits to investors. While the approach used in this article is applied to Islamic equity markets, the methodological framework can also be used for other similar cases in Islamic finance

Functional Oxides with Nitride Buffer Layers for Heteroepitaxial Devices

As conventional memory technologies approach their limit of scalability, there is a quest to find new technologies to replace existing memories. Of the emerging switching phenomena, ferroelectric switching and resistive switching have been considered for this work. Ferroelectricity is a property by which a material develops a spontaneous polarization that can be reversed by and external electric field. Resistive switching, the basis for the novel “memristor” devices, is a property that enables a device switch to a low or high resistance state depending on the magnitude and polarity of the applied voltage. In this work, various nanostructures have been explored to achieve property enhancement in functional oxides. For example, vertically aligned nanocomposite structures consist of two different materials that are simultaneously deposited onto a single substrate, and grow as two distinct phases. Vertically aligned nanocomposite structures offer the advantage of strain tuning through the vertical interfaces between phases. First, to improve the ferroelectric properties of BaTiO3, a conventional ferroelectric material, epitaxial vertically aligned nanocomposite BaTiO3-CeO2 films have been deposited on SrTiO3 substrates. These films exhibit a columnar structure with high epitaxial quality. The films show a similar ferroelectric response as that of pure thin film BaTiO3, but with an improved Curie temperature, despite the incorporation of CeO2. These nanocomposite structures have been replicated on Si substrates using a double buffer layer of SrTiO3/TiN to achieve the eventual integration of these films on Si. No reduction in ferroelectric properties has been observed, but the films again showed an improvement in the Curie temperature. Second, a simple resistive switching device has been demonstrated by the in situ partial oxidation of a TiN film under three different oxidation time periods. The oxidized region consists of near stoichiometric TiO2, and serves as the oxide layer, while the unoxidized TiN serves as the bottom electrode. All films exhibit bipolar resistive switching and all films are forming-free. The forming-free property is attributed to an oxygen deficient TiO2-x layer at the interface between the oxide and nitride regions. Third, ZnO, a piezoelectric, has been selected as another complementary second phase material for BaTiO3. Epitaxial and highly textured vertically aligned BaTiO3-ZnO composite films have been deposited on SrTiO3 substrates and SrTiO3/TiN buffered Si substrates, respectively. Electrical characterization shows that the films grown on both substrates are ferroelectric at room temperature and exhibit similar properties. Composition analysis shows that both the laser fluence and the oxygen partial pressure can modulate the Ba/Ti cation stoichiometry which, in turn, impacts the ferroelectric properties. This is the first demonstration of the vertically aligned nanocomposite of BaTiO3 and ZnO and its silicon based integration. Finally, based on the excellent buffer layer and diffusion barrier properties of TiN for integrating functional oxides on Si, TiN has been applied as a protective layer on metal surfaces. A 500 nm thick TiN layer has been demonstrated to serve as an excellent diffusion barrier in extreme environments