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

I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Principles of Neural Science

This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.

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Phonons and related crystal properties from density-functional perturbation theory

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

The need to develop inexpensive renewable energy sources stimulates scientific research for efficient, low-cost photovoltaic devices.1 The organic, polymer-based photovoltaic elements have introduced at least the potential of obtaining cheap and easy methods to produce energy from light.2 The possibility of chemically manipulating the material properties of polymers (plastics) combined with a variety of easy and cheap processing techniques has made polymer-based materials present in almost every aspect of modern society.3 Organic semiconductors have several advantages: (a) lowcost synthesis, and (b) easy manufacture of thin film devices by vacuum evaporation/sublimation or solution cast or printing technologies. Furthermore, organic semiconductor thin films may show high absorption coefficients4 exceeding 105 cm-1, which makes them good chromophores for optoelectronic applications. The electronic band gap of organic semiconductors can be engineered by chemical synthesis for simple color changing of light emitting diodes (LEDs).5 Charge carrier mobilities as high as 10 cm2/V‚s6 made them competitive with amorphous silicon.7 This review is organized as follows. In the first part, we will give a general introduction to the materials, production techniques, working principles, critical parameters, and stability of the organic solar cells. In the second part, we will focus on conjugated polymer/fullerene bulk heterojunction solar cells, mainly on polyphenylenevinylene (PPV) derivatives/(1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61) (PCBM) fullerene derivatives and poly(3-hexylthiophene) (P3HT)/PCBM systems. In the third part, we will discuss the alternative approaches such as polymer/polymer solar cells and organic/inorganic hybrid solar cells. In the fourth part, we will suggest possible routes for further improvements and finish with some conclusions. The different papers mentioned in the text have been chosen for didactical purposes and cannot reflect the chronology of the research field nor have a claim of completeness. The further interested reader is referred to the vast amount of quality papers published in this field during the past decade.

Conjugated polymer-based organic solar cells

We present a study on the effect of Ge, deposited on Si(111) substrates prior to the 3C-SiC growth, on the stoichiometric composition of 3C-SiC thin layers grown by SSMBE on Si (111) substrates with Ge amount range from 0 to 1 ML. Secondary Ion Mass Spectroscopy (SIMS) depth profile measurements were used to determine the Si/C intensity ratio present in the 3C-SiC layers and for comparison the Si and C ratios measured in the 3C-SiC layers were compared with 6H-SiC and 4H-SiC respectively. SIMS investigations revealed that the Si/C intensity ratio in the epitaxial layers is different from the Si/C ratio of the single crystals. The intensity ratio of the 4H-SiC and 6H-SiC samples is found to be 2.01, thus the ratio for the sample without Ge is found to be 2.33 and decreases slightly with the introduction of Ge to 2.1 for the sample with 1 ML of Ge. It is suggested that this variation is related to a change in the defect densities caused by the Ge incorporation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Ge incorporation on stoichiometric composition of 3C‐SiC thin films grown on Si(111) substrates

We have studied optical transitions (absorption and luminescence) in nominally undoped and Mg-doped GaN deposited by MOCVD and MBE. In the range between 3.0 and 3.4 eV, a variety of well known low-intensity luminescence lines are observed, whose origin is discussed. In particular, by comparing excitation with subgap versus above-gap laser lines as well as by combining optical subgap absorption with spectrally resolved photoconductivity, we identify localized optical transitions occuring in isolated cubic inclusions in the otherwise hexagonal GaN epitaxial layers. Implications of these strucural defects for photocurrent transients are also presented.

Defect transitions in GaN between 3.0 and 3.4 eV

The effect of low energy sputtering under grazing incidence upon the surface composition of SiC was investigated by Auger electron spectroscopy. The energy of the sputtering projectiles (He, Ar) varied from 200 to 1500 eV. Peak shifts to the higher energies with increasing argon ion energy were observed for all silicon and carbon Auger transitions. These shifts were explained by enhanced damage of the surface region within the sampling depth of the Auger electrons. The insensitivity of the Auger peak position to the energy of helium ions indicates that the damage state in the surface region does not change with the increasing energy of helium ions. An increase of the carbon concentration with the decrease of the argon energy was observed. The experiments were accompanied by dynamic Monte Carlo simulations by the TRIDYN code.

Sputtering of SiC with low energy He and Ar ions under grazing incidence

Tunable micro lenses based on boron-doped nanocrystalline diamond and aluminum nitride (AlN) thin films are investigated. It is demonstrated that such a material combination is advantageous for the fabrication of highly transparent, mechanically stable optical components capable to operate at high actuation frequencies. In addition, it is shown that radially segmented AlN piezo-actuators allow for free aspheric deformation of the lens surface. It enables the use of such tunable lenses either in wave front filters or for correction of aberrations induced in complex optical systems.

Oliver Ambacher

Papers

Effect of Ge incorporation on stoichiometric composition of 3C‐SiC thin films grown on Si(111) substrates

Defect transitions in GaN between 3.0 and 3.4 eV

Sputtering of SiC with low energy He and Ar ions under grazing incidence

Piezo-actuated tunable diamond/AlN micro lenses

Novel Layout and Packaging for Lateral, Low-Resistance GaN-on-Si Power Transistors