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

Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

/pdf/self-assembled-monolayers-of-thiolates-on-metals-as-a-form-1neb0hj3k4.pdf

Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

This review focuses on the synthesis, protection, functionalization, and application of magnetic nanoparticles, as well as the magnetic properties of nanostructured systems. Substantial progress in the size and shape control of magnetic nanoparticles has been made by developing methods such as co-precipitation, thermal decomposition and/or reduction, micelle synthesis, and hydrothermal synthesis. A major challenge still is protection against corrosion, and therefore suitable protection strategies will be emphasized, for example, surfactant/polymer coating, silica coating and carbon coating of magnetic nanoparticles or embedding them in a matrix/support. Properly protected magnetic nanoparticles can be used as building blocks for the fabrication of various functional systems, and their application in catalysis and biotechnology will be briefly reviewed. Finally, some future trends and perspectives in these research areas will be outlined.

Magnetic nanoparticles: Synthesis, protection, functionalization, and application

Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

http://science.sciencemag.org/content/sci/345/6196/542.full.pdf

Interface engineering of highly efficient perovskite solar cells

Copyright (c) 1996 Elsevier Science B.V. All rights reserved. Core level line asymmetries for liquid Al, Ga, Ge, In, Sn and Bi have been determined by numerical analysis of XPS core level spectra using Doniach−Sunjic lineshapes. For the pure liquid metals, the asymmetry parameters a have been determined as: Al2p: 0.13, Ga3d: 0.11, Ge3d: 0.09, In4d: 0.12, Sn4d: 0.13 and Bi5d: 0.12. Noziere−De Dominicis theory is used to calculate core line asymmetries from the partial electronic densities of states at the Fermi energy. Good agreement is achieved for systematic changes in both parameters. Experimental Knight shifts of liquid metals are compared with theoretical values for s−p-metals. They support the theoretical s-electron density of states (DOSr data used for calculation. Furthermore a quantitative relation between asymmetry and total DOS at the Fermi energy is proposed to explain the observed increase of asymmetry in Ga upon melting: solid: a=0.06, liquid: a=0.11.

Angular momentum of conduction electron states

One of the most interesting electronic properties exhibited by amorphous alloys of the noble metal-polyvalent element-type is a decrease in the electronic density of states towards the Fermi level, EF. This reduction has been attributed to the enhanced backscattering by the structure of the amorphous phase of nearly free sp-electrons with Fermi momentum. On the other hand, such reduction has also been suggested to result from the hybridization between sp-electrons and noble metal d-states. In order to obtain information about the angular momentum distribution of the electronic states near EF, photoemission experiments have been performed on in situ prepared amorphous AuSn and AuSn films using synchrotron radiation in the energy range of 17–92 eV. A strong photon energy and angular momentum dependence of the photoionization cross-section has been observed. The results clearly demonstrate that (i) sp-states are dominant near EF and (ii) hybridization effects between sp- and d-electrons can be neglected to account for the minimum in the density of states at EF.

Synchrotron radiation study on amorphous AuSb and AuSn

Interface reactions were observed by means of photoelectron spectroscopy during the preparation of Au/Sn bilayers at 77 K. These reactions lead to ultra-thin (0.5–2 nm) amorphous layers with tunable stoichiometry, spanning the same range of compositions as found for the corresponding vapor-quenched amorphous Hume-Rothery alloys. In all cases, structure-induced minima in the electronic density of states at the Fermi level are observed for the intermixed amorphous phases. Since structure-induced minima are a characteristic feature of a Peierls system, the ultra-thin amorphous layers may be discussed as reflecting the transition from a nearly two-dimensional to an isotropic three-dimensional Peierls-distorted system.

Low temperature amorphization at interfaces in layered structures: evidence for a low-dimensional Peierls system

Our investigation of the electrical resistance and the thermoelectric power of thin Au films on top of amorphous Sb films as a function of increasing thickness of the Au film allows us to compare the data with those on amorphous films with increasing Au content. The comparison shows a substantial similarity of the low-temperature data as well as of the annealing behaviour. This gives additional support to the hypothesis of the formation of an amorphous phase at the interface in layered Sb/Au films. The thicknesses of those parts of the Sb film and the Au film which contribute to the formation of the amorphous interface are determined and agree well with data taken from photoelectron spectroscopy and resistance measurements during evaporation. The quantitative differences which exist in the concentration dependence of the electrical resistance and the thermoelectric power between the Sb/Au bilayers and the amorphous films are probably caused by the reduced geometry of the ultrathin interface.

Thermoelectric power and electrical resistance of thin, quench-condensed Sb/Au bilayers - a study of an amorphous phase at the interface

Photoelectron spectra of the 3rd level of liquid and solid Ga have been measured at temperatures between 295 and 819 K using He II resonance radiation (40.8 eV). A numerical least-squares fit analysis revealed a surface-shifted component of the Ga3d levels for solid Ga with relative intensity of 0.25 ± 0.03 at −0.22 ± 0.02 eV lower binding energy. For liquid Ga, no such surface-shifted contribution could be detected at the present level of accuracy. For the Ga3d bulk component (binding energy E B = 18.45 eV), a small shift to lower binding energy of ΔE B = −0.018 ± 0.005 eV was found in liquid Ga with respect to the recrystallized sample.

Hans-Gerd Boyen

Papers

Angular momentum of conduction electron states

Synchrotron radiation study on amorphous AuSb and AuSn

Low temperature amorphization at interfaces in layered structures: evidence for a low-dimensional Peierls system

Thermoelectric power and electrical resistance of thin, quench-condensed Sb/Au bilayers - a study of an amorphous phase at the interface

Surface core level shift for liquid and solid gallium