Femtosecond pulse shaping for phase and morphology control in PLD: Synthesis of cubic SiC

Pulse shaping introduces the method that makes possible the production of tunable arbitrary shaped pulses. We extend this method to control the prevalent growth of cubic SiC films on Si (1 0 0) substrates by pulsed laser deposition at temperatures around 973 K from a SiC target in vacuum. We used a laser system generating 200 fs pulses duration at 800 nm with 600 μJ at 1 kHz. The obtained structures are investigated by electron microscopy, X-ray diffraction and profilometry. We observed grains embedded in an amorphous texture, characteristic in our opinion to the depositions obtained with very short pulses. We present a comparison of deposited films with and without pulse shaping. Pulse shaping promotes increased crystallization and results in the deposition of thin structures of cubic SiC with a strongly reduced density of particulates, under similar deposition conditions.     

Energy Balance of Low-Voltage Spark Discharges

In this work we are presenting an experimental and theoretical analysis of the energy balance of low-voltage spark discharges. It is pointed out that the greatest part of the energy from the central hot plasma region is lost in the form of radiation, but the radiation from electrode particles (here aluminium) can be important, too.     

Surface treatment with linearly polarized laser beam at oblique incidence

An effective method for surface heat treatment with 10.6 μm linear polarized laser beam at oblique incidence is reported. A circular focused laser spot on the workpiece surface, simultaneously with 2.2–4 times increasing of the absorption are obtained in the 70–80° range of the incidence angle. The main element of the experimental setup is the astigmatic focusing head which focalize the laser beam into an elliptical spot of ellipticity >3 at normal incidence. At a proper incidence angle (obtained by the focusing head tilting) the focused laser spot on the work piece surface gets a circular form and p-state of polarization is achieved.We performed laser heat treatment (transformation hardening, surface remelting) of the uncoated surface, as well as the alloying and cladding processes by powder injection. An enhancement of the processing efficiency was obtained; in this way the investment and operation costs for surface treatment with CO₂ laser can be significantly reduced. Several technical advantages concerning the pollution of the focusing optical components, powder jet flowing and reflected radiation by the work piece surface are obtained.     

Pulsed laser deposition of semiconducting crystalline double-doped barium titanate thin films on nickel substrates

We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO₃ and (Ba,Pb,Y)TiO₃ thin films on mechanically polished nickel substrates.The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements.We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature.     

Deposition of antibacterial of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80/gentamicin sulfate composite coatings by MAPLE

We report on thin film deposition of poly(1,3-bis-(p-carboxyphenoxy propane)-co-sebacic anhydride)) 20:80 thin films containing several gentamicin concentrations by matrix assisted pulsed laser evaporation (MAPLE). A pulsed KrF* excimer laser was used to deposit the polymer-drug composite thin films. Release of gentamicin from these MAPLE-deposited polymer conjugate structures was assessed. Fourier transform infrared spectroscopy was used to demonstrate that the functional groups of the MAPLE-transferred materials were not changed by the deposition process nor were new functional groups formed. Scanning electron microscopy confirmed that MAPLE may be used to fabricate thin films of good morphological quality. The activity of gentamicin-doped films against Escherichia coli and Staphylococcus aureus bacteria was demonstrated using disk diffusion and antibacterial drop test. Our studies indicate that deposition of polymer-drug composite thin films prepared by MAPLE is a suitable technique for performing controlled drug delivery. Antimicrobial thin film coatings have several medical applications, including use for indwelling catheters and implanted medical devices.     

Entropy Production for a Class of Inverse SRB Measures

We study the entropy production for inverse SRB measures for a class of hyperbolic folded repellers presenting both expanding and contracting directions. We prove that for most such maps we obtain strictly negative entropy production of the respective inverse SRB measures. Moreover we provide concrete examples of hyperbolic folded repellers where this happens.     

Development of magnetic rotation in light Gd nuclei; study of 142Gd

High-spin states in ¹⁴²Gd have been populated by means of the ⁹⁹Ru(⁴⁸Ti, 2p3n) reaction at 240 MeV and investigated with the γ-spectrometer EUROBALL III and the charged-particle detector array ISIS. The features of four dipole bands have been determined and compared with tilted-axis cranking model calculations indicating that they are magnetic rotational bands. A transition from regular to irregular bands has been found approaching N = 82 demonstrating that this is a general phenomenon in nuclei near a double-shell closure. Received: 9 December 2001 / Accepted: 9 January 2002     

Pseudo-spin band in the odd-odd nucleus 172Lu

High-spin states in the odd-odd nucleus ¹⁷²Lu have been populated in a ¹⁷⁰Er(⁷Li, 5n) reaction and the emitted -radiation was detected with the GASP array. Two sequences of a new identical band have been observed with the transition energies in the favoured and unfavoured sequences being identical within keV at low spins and keV at high spins over the whole observed spin range. Aninterpretation as a pseudo-spin singlet band of configuration is proposed. It represents the best example of a pseudo-spin singlet band in normal deformed nuclei known until now.Received: 19 February 2003, Revised: 27 March 2003, Published online: 12 August 2003PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.70.+q      

Investigations of the level scheme of 144Gd and lifetimes in the quadrupole bands

For a level scheme investigation of ¹⁴⁴Gd an experiment with the -spectrometer EUROBALL III has been carried out and lifetimes have been measured with the -spectrometer GASP using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the ¹⁰⁰Mo(⁴⁸Ti,4n) reaction at 215 MeV and the ¹¹⁴Cd(³⁶S,6n) reaction at E = 182 MeV, respectively. The known quadrupole band has been modified and a new one has been established. Reduced E2 transition probabilities B(E2) were determined for seven members of these quadrupole bands. They show values between and 130 W.u. and this considerable enhancement gives evidence for a significant nuclear deformation. A configuration may be assigned to one of the quadrupole bands according to total Routhian surface calculations. The spin dependence of the B(E2) values has been explained by IBM calculations involving high-spin quasiparticle excitations.Received: 5 June 2003, Revised: 10 December 2003, Published online: 23 July 2004PACS: 21.10.Re Collective levels - 21.10.Tg Lifetimes - 21.60.Fw Models based on group theory - 27.60. + j