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The authors show that infrared imaging of the charge density profile in organic field-effect transistors (FETs) can probe transport characteristics which are difficult to access by conventional contact-based measurements. Specifically, they carry out experiments and modeling of infrared spectromicroscopy of poly-hexylthiophene (FETs) in which charge injection is affected by a relatively low resistance of the gate insulators. They conclude that the mobility of P3HT has a power-law density dependence, which is consistent with the activated transport in disorder-induced tails of the density of states.

We carry out a comprehensive theoretical and experimental study of charge injection in poly(3-hexylthiophene) (P3HT) to determine the most likely scenario for metal-insulator transition in this system. Wecalculate the optical-absorption frequencies corresponding to a polaron and a bipolaron lattice in P3HT. We also analyze the electronic excitations for three possible scenarios under which a first- or a second-order metal-insulator transition can occur in doped P3HT. These theoretical scenarios are compared with data from infrared absorption spectroscopy on P3HT thin-film field-effect transistors (FETs). Our measurements and theoretical predictions suggest that charge-induced localized states in P3HT FETs are bipolarons and that the highest doping level achieved in our experiments approaches that required for a first-order metal-insulator transition.

The terahertz (THz) and sub-THz region of the electromagnetic spectrum bridges the infrared and the microwave. This boundary region is beyond the normal reach of optical and electronic measurement techniques normally associated with these better-known neighbors. Only over the past decade has this THz region become scientifically accessible withbroadband sources of moderate intensity being produced by ultra-fast laser pulses incident on biased semiconductors or non-linear crystals [1,2]. Very recently, a much higher power source of THz radiation was demonstrated: coherent synchrotron radiation (CSR) from short, relativistic electron bunches [3-5]. Coherent synchrotron radiation will open up new territory in the THz frequency range with intensities many orders of magnitude higher than previous sources. The energy range between microwave and the far infrared, 3 33 cm-1 (0.1 1 THz), has proven to be challenging to accesses and is therefore referred to as the THz gap . However, with the new CSR source at BESSY [3,5] we have been able to extend traditional infrared measurements down into this sub-terahertz frequency range. This source is broadband and is made up of longitudinally coherent single-cycle sub-picosecond pulses with a high repetition rate (100 s of MHz). With the combination of high intensity and short pulse duration new opportunities for scientific research and applications are enabled across a diverse array of disciplines from condensed matter physics, to medical, technological, manufacturing, space and defense industries. Imaging, spectroscopy, femtosecond dynamics, and driving novel non-linear processes are all among the potential applications. The high average power of the CSR source allows one to extend experimental conditions to lower frequencies than have been possible with thermal and conventional synchrotron sources (Figure 1). In this paper, we make use of the stable CSR THz source at BESSY for threeinitial scientific demonstration experiments.

The observation and modeling of coherent transition radiation from femtosecond laseraccelerated electron bunches is discussed. The coherent transition radiation, scaling quadratically with bunch charge, is generated as the electrons transit the plasma-vacuum boundary. Due to the limited transverse radius of the plasma boundary, diffraction effects will strongly modify the angular distribution and the total energy radiated is reduced compared to an infinite transverse boundary. The multi-nC electron bunches, concentrated in a length of a few plasma periods (several tens of microns), experience partial charge neutralization while propagating inside the plasma towards the boundary. This reduces the space-charge blowout of the beam, allowing for coherent radiation at relatively high frequencies (several THz). The charge distribution of the electron bunch at the plasma-vacuum boundary can be derived from Fourier analysis of the coherent part of the transition radiation spectrum. A Michelson interferometer was used to measure the coherent spectrum, and electron bunches with duration on the order of 50 fs (rms) were observed.

Coherent radiation in the 0.3 - 3 THz range has been generated from femto second electron bunches at a plasma-vacuum boundary via transition radiation. The bunches produced by a laser-plasma accelerator contained 1.5 nC of charge. The THz energy per pulse within a limited 30 mrad collection angle was 3.5 nJ and scaled quadratically with bunch charge, consistent with coherent emission. Modeling indicates that this broadband source produces about 0.3 muJ per pulse within a 100 mrad angle, and that increasing the transverse plasma size and electron beam energy could provide more than 100 muj/pulse.

We present the concepts for a storage ring dedicated to and optimized for the production of stable coherent synchrotron radiation (CSR) over the far-infrar ed wavelength range from about 200 microns to 1 mm.

Synchrotron-based infrared (IR) microspectroscopy and synchrotron-based x-ray fluorescence have been used to study chemical markers and profiles of latent human fingerprints. IR band intensities and band intensity ratios for functional groups of chemical molecules that are inherent to the experimental system are discussed in the context of molecular species that can be identified by comparison to infrared spectra that have been reported previously in the literature for identified components. The detection and quantitative analysis of electrolytes in the fingerprints is discussed. Mapping of chemical heterogeneities using spectral markers is presented and discussed. Changes in the chemistry of the fingerprint will be discussed in context of the aging process, which is reflected in the changes in the infrared spectra. The use of the technique for chemical and biological profiling of an individual "molecular fingerprint" is also discussed.

Synchrotron-based infrared (IR) microspectroscopy and synchrotron-based x-ray fluorescence have been used to study the chemistry of ink-paper material interactions as a function of both ink type and artificial aging of the ink-papersets as occurs in normal handwriting. IR band intensities and band intensity ratios for functional groups of chemical molecules that are inherent to the experimental system are discussed in the context of molecular components as they are perturbed by interactions between the ink and paper surfaces. Metallic components of some inks and their interactions with the paper are also discussed. Changes in the chemistry of the ink and its related kinetics will be discussed in context of the aging process. This work was supported by the Special Technologies Program, the Center for Science and Engineering Education (CSEE) at Lawrence Berkeley National Laboratory, and by the Director, Office of Science, Office of Basic Energy Sciences, Materials Science Division, of the U. S. Department of Energy under Contract No. DE-ACO3-76SF00098.

This article describes the design rationale, a C implementation, and conformance testing of a subset of the new Standard for the BLAS (Basic Linear Algebra Subroutines): Extended and Mixed Precision BLAS. Permitting higher internal precision and mixed input/output types and precisions allows us to implement some algorithms that are simpler, more accurate, and sometimes faster than possible without these features. The new BLAS are challenging to implement and test because there are many more subroutines than in the existing Standard, and because we must be able to assess whether a higher precision is used for internal computations than is used for either input or output variables. We have therefore developed an automated process of generating and systematically testing these routines. Our methodology is applicable to languages besides C. In particular, our algorithms used in the testing code will be valuable to all other BLAS implementors. Our extra precision routines achieve excellent performance--close to half of the machine peak Megaflop rate even for the Level 2 BLAS, when the data access is stride one.

Research was conducted to investigate the dependence of the fundamental band gap of AlxGa1-xN epitaxial films on Al content and applied hydrostatic pressure. Variation of the band-gap energy resulted from findings of absorption measurements performed at atmospheric pressure. The pressure coefficients for the direct gamma band gaps of AlxGa1-xN were identified through an examination of the pressure dependence of the absorption edge in models with various AlN mole fractions and the compressibility between sapphire substrate and the epitaxial films.