High mobility transistors based on electrospray-printed small-molecule/polymer semiconducting blends

An electrospray-printing technique was employed for the fabrication of OFETs based on small-molecule:semiconducting polymer blends.</p

Second harmonic generation in SiC polytypes

LMTO calculations are presented for the frequency dependent second harmonic generation (SHG) in the polytypes 2H, 4H, 6H, 15R and 3C of SiC. All independent tensor components are calculated. The spectral features and the ratios of the 333 to 311 tensorial components are studied as a function of the degree of hexagonality. The relationship to the linear optical response and the underlying band structure are investigated. SHG is suggested to be a sensitive tool for investigating the near band edge interband excitations.Comment: 12 pages, 10 figure

Optical performance of nanocrystalline transparent Ceria films

Ceria is a transparent oxide suitable for various optical and optoelectronic devices. In this work, we tailor independently the refractive index n and fundamental gap E-g of nanocrystalline Ceria films by varying the substrate temperature or using Ar+ ion beams during growth with electron beam evaporation. Spectroscopic ellipsometry and x-ray reflectivity are employed to study n and E-g and to identify the physical parameters that affect them. We correlate n (varies from 1.65 to 2.15 in the studied films) with the film density through a universal, square law. The film composition strongly affects E-g, which varies from 2.8 to similar to2.0 eV. The optical absorption below 3 eV and the E-g shift are attributed to O-defect states and not to modifications in interband transitions. (C) 2002 American Institute of Physics.Applied Physics Letter

Nanomechanical properties of multilayered amorphous carbon structures

A possible route toward reducing the intrinsic compressive stress in as-grown amorphous carbon films on Si substrates, with a high fraction of tetrahedral bonding, is by forming multilayered a-C structures composed of layers dense and rich in sp(3) sites alternated by layers rich in sp(2) geometries, a type of an amorphous superlattice. We present here a combined theoretical and experimental effort to investigate the stability, stress, and elastic properties of this type of a-C material. Our theoretical approach is based on Monte Carlo simulations within an empirical potential scheme, while the experimental part consists of spectroscopic ellipsometry, x-ray reflectivity, stress, and nanoindentation measurements in films prepared by magnetron sputtering. Our central result is that the average stress in the multilayered structures is nearly eliminated through layer-by-layer stress compensation, yet the fraction of sp(3) sites in the dense regions remains high, sustained by the overwhelmingly compressive local stresses. The sp(3)-rich layers are stable both against a moderate increase of the width of the low-density layers, as well as under thermal annealing. The elastic moduli of the multilayered films are comparable with those of single-layer films. This, in conjuction with their low stress, makes them suitable for mechanical purposes.Physical Review

Many-body calculations of plasmon and phonon satellites in angle-resolved photoelectron spectra using the cumulant expansion approach

The interaction of electrons with crystal lattice vibrations (phonons) and collective charge-density fluctuations (plasmons) influences profoundly the spectral properties of solids revealed by photoemission spectroscopy experiments. Photoemission satellites, for instance, are a prototypical example of quantum emergent behavior that may result from the strong coupling of electronic states to plasmons and phonons. The existence of these spectral features has been verified over energy scales spanning several orders of magnitude (from 50 meV to 15-20 eV) and for a broad class of compounds such as simple metals, semiconductors, and highly-doped oxides. During the past few years the cumulant expansion approach, alongside with the GW approximation and the theory of electron-phonon and electron-plasmon coupling in solids, has evolved into a predictive and quantitatively accurate approach for the description of the spectral signatures of electron-boson coupling entirely from first principles, and it has thus become the state-of-the-art theoretical tool for the description of these phenomena. In this chapter we introduce the fundamental concepts needed to interpret plasmon and phonon satellites in photoelectron spectra, and we review recent progress on first-principles calculations of these features using the cumulant expansion method

Nanoscale Visualization of Elastic Inhomogeneities at TiN Coatings Using Ultrasonic Force Microscopy

Ultrasonic force microscopy has been applied to the characterization of titanium nitride coatings deposited by physical vapor deposition dc magnetron sputtering on stainless steel substrates. The titanium nitride layers exhibit a rich variety of elastic contrast in the ultrasonic force microscopy images. Nanoscale inhomogeneities in stiffness on the titanium nitride films have been attributed to softer substoichiometric titanium nitride species and/or trapped subsurface gas. The results show that increasing the sputtering power at the Ti cathode increases the elastic homogeneity of the titanium nitride layers on the nanometer scale. Ultrasonic force microscopy elastic mapping on titanium nitride layers demonstrates the capability of the technique to provide information of high value for the engineering of improved coatings

Development of scalable and versatile nanomaterial libraries for nanosafety studies: polyvinylpyrrolidone (PVP) capped metal oxide nanoparticles

The potential long-term environmental impact of manufactured nanomaterials (NMs) remains poorly understood, and the need to better predict NM fate and transformations and chronic effects is particularly urgent. Compared to their bulk counterparts, manufactured NMs can have distinct physical and chemical characteristics, which influence their behaviour, stability and toxicity. It is therefore essential to develop standard and reference NM libraries for environmental nanoscience and nano(eco)toxicology, and to facilitate a move towards computational prediction of NM fate, through quantitative structure–activity relationships for example. The aim of this work was to develop and fully characterise one such library, which included comparable NMs with a range of core chemistries, but the same capping agent and size range, for use in future studies to test the hypothesis that the core chemistry is a primary factor in controlling toxicity. The library contained the following NMs: 10k, 40k and 360k PVP capped ceria, zinc oxide and copper oxide (9 NMs in total). The work presented here upholds the underpinning hypothesis that the mechanism of NM formation is the same in all cases, suggesting that the protocol is very robust and has the potential to generate a wide range of comparable metal oxide NMs and potentially expand the library further with doped metal oxide and metal NMs. Characterisation by means of DLS (both size and zeta measurements), UV/Vis, XPS, FT-IR, TEM, STEM, EDX and EELS confirms that the tested synthesis protocol can easily and successfully be used to create stable PVP capped metal oxide NMs of reproducible sizes