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

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Hundreds of different types of coatings are used to protect a variety of structural engineering materials from corrosion, wear, and erosion, and to provide lubrication and thermal insulation. Of all these, thermal barrier coatings (TBCs) have the most complex structure and must operate in the most demanding high-temperature environment of aircraft and industrial gas-turbine engines. TBCs, which comprise metal and ceramic multilayers, insulate turbine and combustor engine components from the hot gas stream, and improve the durability and energy efficiency of these engines. Improvements in TBCs will require a better understanding of the complex changes in their structure and properties that occur under operating conditions that lead to their failure. The structure, properties, and failure mechanisms of TBCs are herein reviewed, together with a discussion of current limitations and future opportunities.

http://science.sciencemag.org/content/sci/296/5566/280.full.pdf

Thermal Barrier Coatings for Gas-Turbine Engine Applications

BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

Physics and Applications of Bismuth Ferrite

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Functional gradation is one characteristic feature of living tissue. Bio-inspired materials open new approaches for manufacturing implants for bone replacement. Different routes for new implant materials are presented using the principle of functional gradation. An artificial biomaterial for knee joint replacement has been developed by building a graded structure consisting of ultra-high molecular weight polyethylene (UHMWPE) fibre reinforced high-density polyethylene combined with a surface of UHMWPE. The ingrowth behaviour of titanium implants into hard tissue can be improved by depositing a graded biopolymer coating of fibronectin, collagen types I and III with a gradation, derived from the mechanisms occurring during healing in vivo. Functionally graded porous hydroxyapatite (HAP) ceramics can be produced using alternative routes, e.g. sintering of laminated structures of HAP tapes filled with polymer spheres or combining biodegradable polyesters such as polylactide, polylactide-co-glycolide and polyglycolide, with carbonated nanocrystalline hydroxyapatite. HAP–collagen I scaffolds are an appropriate material for in vitro growth of bone. The scaffold has to be functionally graded in order to create an optimised mechanical behaviour as well as the intended improvement of the cell ingrowth.

Functionally graded materials for biomedical applications

Possible mechanisms for strain relaxation in ferroelectric thin films are developed. The models are applicable to tetragonal thin film ferroelectrics grown epitaxially on (001) cubic single crystal substrates. We assume growth at temperatures in excess of the Curie temperature (Tc). The extent of strain accommodation by misfit dislocations is considered at the growth temperature (Tg). On cooling to Tc, further misfit dislocation generation is possible due to differences in thermal expansion behavior of the film and substrate. During the paraelectric to ferroelectric transition (PE→FE) additional strains develop in the film. The total strain for the FE phase may be relieved either by further misfit generation or by domain formation. We have developed temperature dependent stability maps that predict the stable domain structure that forms during the PE→FE transition. The stability maps incorporate the role of the following parameters: (i) substrate lattice parameter, (ii) differential thermal expansion characteristics between the film and substrate, (iii) cooling rate, and (iv) depolarizing fields and electrode geometry. Further, the role of dislocation stabilization of domain patterns is discussed.

Domain configurations due to multiple misfit relaxation mechanisms in epitaxial ferroelectric thin films. i: theory

A magnetite colloid was prepared in alkaline solution according to the procedure published by Massart [11]. An aqueous solution containing 2.3 g (8.5 mmol) FeCl 3 ×6H 2 O in 4 mL H 2 O and 1.69 g (4.3 mmol) Fe(NH 4) 2 (SO 4) 2 in 1 mL of 2 M HCl, was added to 50 mL of 1 M (CH 3) 4 NOH×5H 2 O. The resulting black suspension was stirred for 1 h at room temperature and then sonicated in an ultrasonic bath for 1 h. The colloid was then centrifuged at 20 000 g for 1 h. The supernatant was decanted and the slurry resuspended in 20 mL water by sonication before being passed through a 0.2 mm pore cellulose nitrate membrane. A titanium dioxide sol was prepared by hydrolysis of titanium tetraiso-propoxide under a nitrogen atmosphere following the procedure described by O'Regan et al. [12]. 25 mL of titanium tetraisopropoxide was mixed with 4 mL of isopropanol in a dropping-funnel under a nitrogen atmosphere. This mixture was added slowly over a period of 5 min to 150 mL of vigorously stirred double-distilled, deionized water in a 250 mL three-neck flask equipped with heater, thermometer and stirrer. Ten minutes after the final alkoxide addition, 1 mL of 69 % HNO 3 was added. The white hydrolysis mixture was then stirred for 8 h at 80 C to remove the isopropanol, filtered through a 0.2 mm pore cellulose nitrate membrane, and sonicated for 1 h to produce a stable colloidal solution with a bluish-white coloration. Preparation of the Composites and Method of Calcination: Typically, a sample of the sliced copolymer gel (ca. 5 mm thick) was added to the colloidal sol and left for the desired period of time. The colloid-loaded gels were removed, washed with water and allowed to dry in air. Thermogravi-metric analysis (TGA) measurements were made using a NETZSCH STA 409EP machine. Samples were heated under air in an alumina crucible to a final temperature of 800 C at a rate of 5 K/min. Large samples of the miner-alized gels were calcined by heating to a temperature of 450 or 500 C in a Carbolite furnace (type ELF11/6) at a heating rate of 1 C min ±1. Analytical Methods: The morphology of the copolymer gel in the water-swollen state was examined using a Jeol 6310 SEM equipped with a cryo-stage and energy-dispersive X-ray (EDX). …

Nanoscale palladium metallization of DNA

We present measurements of the electrical conductivity of metallic nanowires which have been fabricated by chemical deposition of a thin continuous palladium film onto single DNA molecules to install electrical functionality. The DNA molecules have been positioned between macroscopic Au electrodes and are metallized afterwards. Low-resistance electrical interfacing was obtained by pinning the nanowires at the electrodes with electron-beam-induced carbon lines. The investigated nanowires exhibit ohmic transport behavior at room temperature. Their specific conductivity is only one order of magnitude below that of bulk palladium, confirming that DNA is an ideal template for the production of electric wires, which can be utilized for the bottom-up construction of miniaturized electrical circuits.

/pdf/construction-of-highly-conductive-nanowires-on-a-dna-2rjili4wgw.pdf

Construction of highly conductive nanowires on a DNA template

To find new ways for the synthesis of improved bone implant materials, we studied the mineralization of collagen in vitro. Collagen was mineralized by combining the collagen fibril assembly and the formation of calcium phosphate in one process step. Both reactions were initiated simultaneously by mixing an acid, calcium-containing collagen solution with a phosphate-containing neutralization buffer. Under suitable conditions first fibril assembly occurred along with the precipitation of an amorphous calcium phosphate phase. Subsequently, the amorphous calcium phosphate transformed into a crystalline, apatite-like phase, as revealed by IR spectroscopy and X-ray diffraction. In this way, a homogeneously mineralized collagen gel was obtained, consisting of a three-dimensional network of collagen fibrils covered with calcium phosphate. The attachment between the collagen fibrils and the calcium phosphate crystals could be further improved by the addition of polyaspartate to the reaction mixture. In the absence...

Wolfgang Pompe

Papers

Functionally graded materials for biomedical applications

Domain configurations due to multiple misfit relaxation mechanisms in epitaxial ferroelectric thin films. i: theory

Nanoscale palladium metallization of DNA

Construction of highly conductive nanowires on a DNA template

Biomimetic mineralization of collagen by combined fibril assembly and calcium phosphate formation