Recent Advances in TiO2 Nanotube-Based Materials for Photocatalytic Applications Designed by Anodic Oxidation

This book chapter reports some spectacular and interesting 1D nanostructures of TiO2, which are grown by the anodic oxidation. Under suitable conditions, conventional one-step anodic oxidation is available to grow TiO2 nanotube arrays (TNAs) and TiO2 nanowires/nanotubes; meanwhile, two-step anodic oxidation allows fabricating some novel TNAs with spectacular morphologies such as highly ordered TNAs, bamboo-type TNAs, and lotus root-shaped TNAs. The formation mechanisms of these nanostructures during the anodic oxidation processes are elusive via studying effects of several key parameters such as oxidizing voltage, processing time, and electrolytes. In addition, the photocatalytic activity of the TNA-based nanomaterials is characterized by the degradation of pharmaceutical model, methylene blue, or the photoelectrochemical effect

Ultrafast Dynamics in Topological Insulators

Ultrafast dynamics of carriers and phonons in topological insulator Bi2Se3, CuxBi2Se3 (x = 0, 0.1, 0.125) single crystals were studied by time-resolved pump-probe spectroscopy. The coherent optical phonon (A1g1) is found via the damped oscillation in the transient reflectivity changes (∆R/R) for CuxBi2Se3. The observed red shift of A1g1 phonon frequency suggests the intercalation of Cu atoms between a pair of the quintuple layers of Bi2Se3 crystals. Moreover, the relaxation processes of Dirac fermion near the Dirac point of Bi2Se3 are studied by optical pump and mid-infrared probe spectroscopy through analyzing the negative peak of the ∆R/R. The Dirac fermion-phonon coupling strength was found in the range of 0.08–0.19 and the strength is reduced as it gets closer to the Dirac point. The ultrafast dynamics and fundamental parameters revealed by time-resolved pump-probe spectroscopy are important for designing the optoelectronics in the mid-IR and THz ranges

Nanostructuring Indium-Tin-Oxide Thin Films by Femtosecond Laser Processing

This chapter reviews the nanostructuring fabrications and properties of indium-tin-oxide (ITO) thin films by femtosecond laser annealing. Fundamental mechanisms of laser-induced periodic surface structures (LIPSS) and other nanostructures on ITO films are presented and discussed in detail. ITO films with large-area surface ripple structures with a multiperiodic spacing of ~800, ~400, and ~200 nm were successfully fabricated by femtosecond laser pulses, without scanning. The ITO films exhibited significant enhancement in electrical conductivity by ~30 times because of the formation and distribution of indium metal-like clusters. This metallic content of the laser-induced nanodots and nanolines further causes the anisotropic transmission characteristics in the visible range. In addition, by varying the laser fluences, nanostructures with cotton, brick, and ripple forms are generated on the surface of ITO films, which produce cyan, yellow, and orange colors. Intriguingly, the ITO films with laser-induced nanostructures can significantly attenuate blue light, thus they are potential for applications such as eye protection and information security

Thermoelectric and Topological Insulator Bismuth Chalcogenide Thin Films Grown Using Pulsed Laser Deposition

Bismuth chalcogenides have been intensively studied for their high-performance thermoelectric properties and their novel topological surface states, which could significantly benefit novel applications in fields such as TE devices, spintronics, and quantum computing. This chapter reports recent advances in pulsed laser deposition (PLD) for the growth of bismuth chalcogenide (e.g., Bi2Te3, Bi2Se3, and Bi3Se2Te) thin films and their novel properties. It covers a wide range of fields such as thin film growth using PLD for fabricating polycrystalline and epitaxial films with different thermoelectric, nanomechanical, and magnetotransport properties as a function of the PLD processing conditions. Moreover, the proximity-induced superconductivities in Bi inclusions/bismuth chalcogenide thin films are also reported and discussed in detail

Solving parametric systems of polynomial equations over the reals through Hermite matrices

We design a new algorithm for solving parametric systems having finitely many complex solutions for generic values of the parameters. More precisely, let $f = (f_1, \ldots, f_m)\subset \mathbb{Q}[y][x]$ with $y = (y_1, \ldots, y_t)$ and $x = (x_1, \ldots, x_n)$, $V\subset \mathbb{C}^{t+n}$ be the algebraic set defined by $f$ and $\pi$ be the projection $(y, x) \to y$. Under the assumptions that $f$ admits finitely many complex roots for generic values of $y$ and that the ideal generated by $f$ is radical, we solve the following problem. On input $f$, we compute semi-algebraic formulas defining semi-algebraic subsets $S_1, \ldots, S_l$ of the $y$-space such that $\cup_{i=1}^l S_i$ is dense in $\mathbb{R}^t$ and the number of real points in $V\cap \pi^{-1}(\eta)$ is invariant when $\eta$ varies over each $S_i$. This algorithm exploits properties of some well chosen monomial bases in the algebra $\mathbb{Q}(y)[x]/I$ where $I$ is the ideal generated by $f$ in $\mathbb{Q}(y)[x]$ and the specialization property of the so-called Hermite matrices. This allows us to obtain compact representations of the sets $S_i$ by means of semi-algebraic formulas encoding the signature of a symmetric matrix. When $f$ satisfies extra genericity assumptions, we derive complexity bounds on the number of arithmetic operations in $\mathbb{Q}$ and the degree of the output polynomials. Let $d$ be the maximal degree of the $f_i$'s and $D = n(d-1)d^n$, we prove that, on a generic $f=(f_1,\ldots,f_n)$, one can compute those semi-algebraic formulas with $O^~( \binom{t+D}{t}2^{3t}n^{2t+1} d^{3nt+2(n+t)+1})$ operations in $\mathbb{Q}$ and that the polynomials involved have degree bounded by $D$. We report on practical experiments which illustrate the efficiency of our algorithm on generic systems and systems from applications. It allows us to solve problems which are out of reach of the state-of-the-art

Computing totally real hyperplane sections and linear series on algebraic curves

Given a real algebraic curve, embedded in projective space, we study the computational problem of deciding whether there exists a hyperplane meeting the curve in real points only. More generally, given any divisor on such a curve, we may ask whether the corresponding linear series contains an effective divisor with totally real support. This translates into a particular type of parametrized real root counting problem that we wish to solve exactly. On the other hand, it is known that for a given genus and number of real connected components, any linear series of sufficiently large degree contains a totally real effective divisor. Using the algorithms described in this paper, we solve a number of examples, which we can compare to the best known bounds for the required degree

Recent Advances in BiVO4- and Bi2Te3-Based Materials for High Efficiency-Energy Applications

This chapter provides recent progress in developments of BiVO4- and Bi2Te3-based materials for high efficiency photoelectrodes and thermoelectric applications. The self-assembling nanostructured BiVO4-based materials and their heterostructures (e.g., WO3/BiVO4) are developed and studied toward high efficiency photoelectrochemical (PEC) water splitting via engineering the crystal and band structures and charge transfer processes across the heteroconjunctions. In addition, crystal and electronic structures, optical properties, and strategies to enhance photoelectrochemical properties of BiVO4 are presented. The nanocrystalline, nanostructured Bi2Te3-based thin films with controlled structure, and morphology for enhanced thermoelectric properties are also reported and discussed in details. We demonstrate that BiVO4-based materials and Bi2Te3-based thin films play significant roles for the developing renewable energy

Recent Advances in Pt-Based Binary and Ternary Alloy Electrocatalysts for Direct Methanol Fuel Cells

The direct methanol fuel cell (DMFC) is among the most promising alternative energy sources for the near future owing to its advantages of simple construction, compact design, high energy density, and relatively high energy-conversion efficiency. Typically, the electrodes in DMFC is comprised of a Pt-based catalysts supported on great potential of carbon materials such as multi-walled carbon nanotubes (MWCNTs), carbon black (CB), graphene, etc. It is desired to develop an electrode with high surface area, good electrical conductivity and suitable porosity to allow good reactant flux and high stability in the fuel cell environment. This chapter will provide recent advances in Pt-based binary and ternary electrocatalysts on carbon supports for high-performance anodes in DMFC. Through studying the effects of composition-, support-, and shape dependent electrocatalysts, further fundamental understanding and mechanism in the development of anode catalysts for DMFC will be provided in details

The Effectiveness of Applying Realistic Mathematics Education Approach in Teaching Statistics in Grade 7 to Students' Mathematical Skills

The research was carried out to verify the effectiveness of applying Realistic Mathematics Education (RME) on the development of skills required by students in statistical content in grade 7. For achieving research objectives, the pedagogical experiment was conducted in the form of intrinsic legalization for forty-eight 7th-grade students at Tang Phu Nhan B Junior School, District 9, Ho Chi Minh City, Vietnam. Accordingly, data on pre-test results, study sheets, post-test, and student learning performance were collected and analyzed qualitatively. The results were assessed based on the criteria corresponding to the required skills for the statistical content, including the criteria for data collection, classification, and representation according to the given criteria for the skill, data collection, and organization capabilities; simple problem formation and problem-solving criteria arise from the existing statistical figures and charts for data analysis and processing skills. The primary mathematical statistics method was used to evaluate the achievement level of students for each criterion. Thereby, the experimental results showed that applying the RME approach in teaching statistical content positively impacted the development of some skills that students needed to achieve. Also, a number of guidelines were provided to guide the enhancement of RME activities