There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Generations Yi Ma,† Xiuli Wang,† Yushuai Jia,† Xiaobo Chen,‡ Hongxian Han,*,† and Can Li*,† †State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Dalian National Laboratory for Clean Energy, 457 Zhongshan Road, Dalian 116023, China ‡Department of Chemistry, College of Arts and Sciences, University of Missouri-Kansas City, 5100 Rockhill Road, Kansas City, Missouri 64110, United States

Titanium dioxide-based nanomaterials for photocatalytic fuel generations.

■ CONTENTS General Information: Books, Reviews, and Conferences 640 Fundamentals 641 Interaction of Laser Beam with Matter 641 Factors Affecting Laser Ablation and LaserInduced Plasma Formation 642 Influence of Target on the Laser-Induced Plasmas 642 Influence of Laser Parameters on the LaserInduced Plasmas 643 Laser Wavelength (λ) 643 Laser Pulse Duration (τ) 643 Laser Pulse Energy (E) 645 Influence of Ambient Gas on the Laser-Induced Plasmas 645 LIBS Methods 647 Double Pulse LIBS 647 Femtosecond LIBS 651 Resonant LIBS 652 Ranging Approaches 652 Applications 654 Surface Inspection, Depth Profiling, and LIBS Imaging 654 Cultural Heritage 654 Industrial Analysis 655 Environmental Monitoring 656 Biomedical and Pharmaceutical Analysis 658 Security and Forensics 659 Analysis of Liquids and Submerged Solids 660 Space Exploration and Isotopic Analysis 662 Space Exploration 662 Isotopic Analysis 662 Conclusions and Future Outlook 663 Author Information 664 Corresponding Author 664 Notes 664 Biographies 664 Acknowledgments 664 References 664

Laser-induced breakdown spectroscopy.

Laser-based additive manufacturing (LBAM) processes can be utilized to generate functional parts (or prototypes) from the ground-up via layer-wise cladding – providing an opportunity to generate complex-shaped, functionally graded or custom-tailored parts that can be utilized for a variety of engineering applications. Directed Energy Deposition (DED), utilizes a concentrated heat source, which may be a laser or electron beam, with in situ delivery of powder- or wire-shaped material for subsequent melting to accomplish layer-by-layer part fabrication or single-to-multi layer cladding/repair. Direct Laser Deposition (DLD), a form of DED, has been investigated heavily in the last several years as it provides the potential to (i) rapidly prototype metallic parts, (ii) produce complex and customized parts, (iii) clad/repair precious metallic components and (iv) manufacture/repair in remote or logistically weak locations. DLD and Powder Bed Fusion-Laser (PBF-L) are two common LBAM processes for additive metal part fabrication and are currently demonstrating their ability to revolutionize the manufacturing industry; breaking barriers imposed via traditional, ‘subtractive’ metalworking processes. This article provides an overview of the major advancements, challenges and physical attributes related to DLD, and is one of two Parts focused specifically on DLD. Part I (this article) focuses on describing the thermal/fluidic phenomena during the powder-fed DLD process, while Part II focuses on the mechanical properties and microstructure of parts manufactured via DLD. In this current article, a selection of recent research efforts – including methodology, models and experimental results – will be provided in order to educate the reader of the thermal/fluidic processes that occur during DLD, as well as providing important background information relevant to DLD as a whole. The thermal/fluid phenomena inherent to DLD directly influence the solidification heat transfer which thus impacts the part's microstructure and associated thermo-mechanical properties. A thorough understanding of the thermal/fluid aspects inherent to DLD is vital for optimizing the DLD process and ensuring consistent, high-quality parts.

An overview of Direct Laser Deposition for additive manufacturing; Part I: Transport phenomena, modeling and diagnostics

Hydrogen (H2) production via photocatalytic water splitting is one of the most promising technologies for clean solar energy conversion to emerge in recent decades. The achievement of energy production from water splitting would mean that we could use water as a fuel for future energy need. Among the various photocatalytic materials, titanium dioxide (TiO2) is the dominant and most widely studied because of its exceptional physico-chemical characteristics. Surface decoration of metal/non-metal on TiO2 nanoparticles is an outstanding technique to revamp its electronic properties and enrich the H2 production efficiency. Metal dopants play a vital role in separation of electron-hole pairs on the TiO2 surface during UV/visible/simulated solar light irradiation. In this paper, the basic principles, photocatalytic-reactor design, kinetics, key findings, and the mechanism of metal-doped TiO2 are comprehensively reviewed. We found that Langmuir-Hinshelwood kinetic model is commonly employed by the researchers to demonstrate the rate of H2 production. Copper (Cu), gold (Au) and platinum (Pt) are the most widely studied dopants for TiO2, owing to their superior work function. The metal dopants can amplify the H2 production efficiency of TiO2 through Schottky barrier formation, surface plasmon resonance (SPR), generation of gap states by interaction with TiO2 VB states. The recent advances and important consequences of 2D materials, perovskites, and other novel photocatalysts for H2 generation have also been reviewed.

Photocatalytic hydrogen production using metal doped TiO2: A review of recent advances

This paper reports optical and nanomechanical properties of predominantly a-axis oriented AlN thin films. These films were deposited by reactive DC magnetron sputtering technique at an optimal target to substrate distance of 180 mm. X-ray rocking curve (FWHM = 52 arcsec) studies confirmed the preferred orientation. Spectroscopic ellipsometry revealed a refractive index of 1.93 at a wavelength of 546 nm. The hardness and elastic modulus of these films were 17 and 190 GPa, respectively, which are much higher than those reported earlier can be useful for piezoelectric films in bulk acoustic wave resonators. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4772204]

Nanomechanical and optical properties of highly a-axis oriented AlN films

Significance of Al on the morphological and optical properties of Ti1−xAlxN thin films

We report a systematic study to determine local elastic properties of surfaces using atomic force acoustic microscopy(AFAM). AFAM is a combination of atomic force microscopy (AFM) and acoustic waves. We describe the technique and principle of AFAM in detail and interpret the obtained images using simple arguments. We have used (1) polished commercial piezoelectric PZT, Pb(Zr,Ti)O3 ceramic, (2) thin film of PZT deposited by the sol?gel technique and (3) thin film of Au deposited on a Si(0?0?1) substrate to elucidate the capability of the AFAM technique to image the distribution of local stiffness over the sample surface. We have also used a complementary technique such as force?distance measurements using the AFM mode to support the interpretation of the AFAM images. We have determined semi-quantitatively the change in the local stiffness over the sample surface using both the force?distance measurement and the change in the contact resonance peak frequency at various regions. We have also shown that the AFAM technique can be used to get a better surface image contrast where contact mode AFM shows poor contrast.

Imaging distribution of local stiffness over surfaces using atomic force acoustic microscopy

Microstructure of turbostratic graphite consists of a large amount of pores and voids which eventually convert to plates and flakes constituting layered microfolding upon high-temperature heat treatment. This treatment results in apparent phase transformation from 3D to 2D structured graphite where stacking order between adjacent layers is absent. Interestingly, low friction coefficients 0.08 and 0.06 were measured in 2D graphite in ambient atmosphere. This is explained in terms of passivation of carbon dangling bonds by the formation of C–O and C–OH where both physisorbed and chemisorbed oxygen species are present. In contrast, these values were as high as 0.17 and 0.19 in 3D graphite. At significantly less humid atmosphere, progressive increase of friction coefficient (up to the value of 0.8) with sliding distance is observed in both 3D and 2D graphites. This consistent increase in friction coefficient is ascribed to gradual loss of residual passivating chemical species such as oxygen and H2O molecules due to tribochemical reaction. Interestingly, the structure of graphite remains similar while Raman spectra obtained from the locations of wear track, where ultra-low and high friction coefficient is measured.

High-temperature phase transformation and low friction behaviour in highly disordered turbostratic graphite

A modified electron beam evaporator has been used to synthesise TiN thin films with (111) preferred orientation. This new design involved in creating local plasma by accelerating the secondary electrons emitted from the evaporating ingot by a positively biased semi-cylindrical anode plate (biased activated reactive evaporation). To accelerate the reaction to form TiN, a jet of gas has been focused towards the substrate as a reactive gas. We have observed a preferred orientation (111) with to the surface normal in pole figure analysis. The residual stress by the classical sin technique did not yield any tangible result due to the preferred orientation. The hardness and modulus measured by nanoindentation technique was around 19.5 and 214 GPa. The continuous multicycle indentation test on these films exhibited a stress relaxation.

Sitaram Dash

Papers

Nanomechanical and optical properties of highly a-axis oriented AlN films

Significance of Al on the morphological and optical properties of Ti1−xAlxN thin films

Imaging distribution of local stiffness over surfaces using atomic force acoustic microscopy

High-temperature phase transformation and low friction behaviour in highly disordered turbostratic graphite

Preferentially oriented electron beam deposited TiN thin films using focused jet of nitrogen gas