The generation of free carriers in CdTe by radiation

This paper presents the results of the quantum efficiency measurement of CdTe over the photon energy range 1·5–4·5 eV obtained from the photovoltaic effect on special photodiodes. There are two kinks observable in the increase of the quantum efficiency which can be explained on the basis of the band structure of CdTe. The first is due to electron, the second due to hole ionization.I wish to thank Prof. E.Klier and Doc. R.Kuel, CSc. for their valuable discussions and Ing. P.Polívka, CSc. for the preparation of CdTe single crystals.     

Mass spectrometric and pyrolytic studies of diphenylarsine derivatives

The trivalent diphenylarsine derivatives studied gave molecular ions and diagnostic common fragment ions at m/e 229, 227, 154, 153, 152, 151, 77 and 51. The diphenylarsine odd electron ion, m/e 229, undergoes the “ortho coupling” reaction before splitting off the arsenic atom. The correlation between the ion fragmentation and the pyrolytic decompositions is discussed.     

Investigation of droplet formation in pulsed Nd:YAG laser deposition of metals and silicon

In the process of pulsed laser deposition of nickel (Ni) and ruthenium (Ru) thin films, the occurrence of phase explosion in ablation was found to affect the deposition rate and enhance the optical emissions from the plasma plume. Faster thin-film growth rates coincide with the onset of phase explosion as a result of superheating and/or sub-surface boiling which also increased the particulates found on the thin-film surface. These particulates were predominantly droplets which may not be round but flattened and also debris for the case of silicon (Si) ablation. The droplets from Ni and Ru thin films were compared in terms of size distribution and number density for different laser fluences. The origins of these particulates were correlated to the bubble and ripple formations on the targets while the transfer to the thin film surface was attributed to the laser-induced ejection from the targets.     

A new method of resolving transient stresses in dynamic holophotoelasticity

A method which allows the simultaneous separation of the isochromatic and isopachic fringes for transient plane-stress problems is presented. A double pulsed ruby laser and a terbium glass Faraday rotator is employed to resolve the transient isochromatic and isopachic patterns. Separated fringe patterns for a structural component are recorded at nine different instants after impact loading. The dynamic material-fringe values of isochromatics and isopachics are obtained within the experiment. Finally, dynamic stresses distributed along a section at different time intervals are resolved.     

Direct current magnetron sputter-deposited ZnO thin films

Zinc oxide (ZnO) is a very promising electronic material for emerging transparent large-area electronic applications including thin-film sensors, transistors and solar cells. We fabricated ZnO thin films by employing direct current (DC) magnetron sputtering deposition technique. ZnO films with different thicknesses ranging from 150 nm to 750 nm were deposited on glass substrates. The deposition pressure and the substrate temperature were varied from 12 mTorr to 25 mTorr, and from room temperature to 450 °C, respectively. The influence of the film thickness, deposition pressure and the substrate temperature on structural and optical properties of the ZnO films was investigated using atomic force microscopy (AFM) and ultraviolet-visible (UV-Vis) spectrometer. The experimental results reveal that the film thickness, deposition pressure and the substrate temperature play significant role in the structural formation and the optical properties of the deposited ZnO thin films.     

Synthesis of polyfunctionalized pyrroles bearing C-2 α-azido side-chains and displacement of the α-azido group by various nucleophiles

Tetrasubstituted pyrroles bearing C-2 α-azido side-chains were synthesized employing a new class of diazides, α,γ-diazido α,β-unsaturated esters, and 1,3-dicarbonyl compounds under simple thermal conditions. Further investigation of the synthetic utility of the obtained pyrroles reveals unexpected displacement of the α-azido group at the C-2 side-chain by a variety of nucleophiles. This two-step process exhibits a broad substrate scope, good functional group tolerance, simple operation, and high reaction efficiency, providing an easy access to polyfunctional pyrroles with novel substitution patterns.     

Characterization of Fluorene - Thiophene Copolymer Layers by the Surface Photovoltage Method

Summary : The surface photovoltage method was used for the study of thin polymer layers made of poly{(9,9-dihexylfluorene-2,7-diyl)[-3-(3-methylbutyl)thiophene-2,5-diyl]} prepared by spin-coating on ITO coated glass substrates. The surface photovoltage (SPV) in a thin polymer layer is a result of dissociation of photogenerated free excitons in electric field of the space charge region (SCR) which forms spontaneously at the surface. The photovoltage signal was formed between a transparent electrode capacitively coupled to the surface of the sample and the back ITO electrode. Photovoltaic spectra were measured under illumination both the free surface (SPV_fs) and the substrate (SPV_ITO) side and for various layer thicknesses. The shape of the SPV_ITO spectrum is very similar to that of the absorption spectrum, whereas the SPV_fs spectrum maximum is shifted to longer wavelengths. Fitting theory to the experimental data, the thickness of the space charge region and the diffusion lengths were evaluated. The results are discussed also in relation to photoluminescence study of thin films.     

The effects of sodium in ITO by pulsed laser deposition on organic light-emitting diodes

The depth profile of ITO on glass was measured by the time-of-flight secondary ion mass spectroscopy (TOFSIMS) which revealed high sodium (Na) ion concentration at the ITO surface as well as at the ITO–glass interface as a result of out diffusion with substrate heating. Effects of Na ions on the performance of organic light-emitting diode (OLED) were studied by etching away a few tens of nanometers off the ITO surface with a dilute aquaregia solution of HNO₃:HCl:H₂O. A single-layer, molecularly doped ITO/(PVK+TPD+Alq₃)/Al OLEDs were fabricated on bare and etched ITO samples. Although the removal of a 10-nm layer of ITO surface increased the voltage range, brightness, and lifetime, it was insufficient to correlate these improvements with solely to the Na ion reduction without considering the surface roughness.     

Effects of laser fluence on the structural properties of pulsed laser deposited ruthenium thin films

Ruthenium (Ru) has received great interest in recent years for applications in microelectronics. Pulsed laser deposition (PLD) enables the growth of Ru thin films at low temperatures. In this paper, we report for the first time the characterization of pulsed laser deposited Ru thin films. The deposition processes were carried out at room temperature in vacuum environment for different durations with a pulsed Nd:YAG laser of 355-nm laser wavelength, employing various laser fluences ranging from 2 J/cm² to 8 J/cm². The effect of the laser fluence on the structural properties of the deposited Ru films was investigated using surface profilometry, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Ru droplets, some spherical in shape and some flattened into round discs were found on the deposited Ru. The droplets were correlated to ripple formations on the target during the laser-induced ejection from the target. In addition, crystalline Ru with orientations of (100), (101), and (002) was observed in the XRD spectra and their intensities were found to increase with increasing laser fluence and film thickness. Grain sizes ranging from 20 nm to 35 nm were deduced using the Scherrer formula. Optical emission spectroscopy (OES) and energy-dispersive X-ray spectroscopy (EDS) show that the composition of the plume and the deposited Ru film was of high purity.