T.M. Di Palma

Chirality and intermolecular forces: studies using R2PI experiments in supersonic beams

One- and two-color, mass-selected resonant two-photon ionization (R2PI) spectra of the S1←S0 transitions in the bare (R)-(+)-1-phenylethan-1-ol (ER) and its complexes with a solvent molecule (solv: (S)-(+)butan-2-ol (BS), (R)-(−)butan-2-ol (BR), or water (W)) have been recorded after a supersonic molecular beam expansion. The excitation spectrum of bare ER conforms to theoretical predictions at the B3LYP/6-31G** level of theory by pointing to the formation of a single conformer. The one-color R2PI excitation spectra of the diastereomeric complexes [ER–solv] (solv: BS or BR) are characterized by significant shifts of their band origin relative to that of bare ER. The extent and the direction of these spectral shifts are found to depend upon the structure and the configuration of solv and are attributed to different short-range interactions in the ground and excited [ER–solv] complexes. In analogy with strictly related diastereomeric complexes, the phenomenological binding energy of the homochiral [ER–BR] is found to be greater that of the heterochiral one [ER–BS]. The one-color R2PI excitation spectra of the [ER–W] complex displays two signals blue shifted by 54 and 73 cm−1, relative to the S1←S0 band origin of bare ER, which indicate the presence of a O–H···π electrostatic interaction between ER and W.

AIN thin film deposition by pulsed laser ablation of Al in NH3

Abstract Aluminium nitride films were synthesized by reaction of laser-evaporated Al in NH3 atmosphere. Optical multichannel emission spectroscopy (OMA) and intensified charge coupled device (ICCD) imaging have been applied to in situ identification of deposition precursors in the plasma plume moving from the target to the substrate. Mass spectrometry has also been used to detect ionic species ejected from an Al target in a mixture with NH3. Thin films prepared by this method were characterized by conventional techniques such as Auger, energy dispersive analysis of X-ray (EDAX), scanning electron microscopy (SEM), and X-ray diffraction. Highly oriented films of AIN (100) on Si (100) were identified.

Reactive pulsed laser ablation and deposition of thin indium tin oxide films for solid state compact sensors

Thin indium tin oxide (ITO) films have been deposited on Si (100) substrates by laser ablating pure metals in oxygen atmosphere. The ablation has been carried out by a frequency doubled Nd:YAG laser and the oxygen pressure has been varied between 50 and 500 Pa. The substrate temperature has been varied from 25 to 700°C. The gaseous phase has been studied by mass spectrometry and fast ICCD imaging. The deposited films have been analysed by X-ray diffraction, scanning electron microscopy and electric resistance measurements.

Composition and gas dynamics of laser ablated AlN plumes

Abstract The formation, composition and propagation of pulsed laser produced plasma plumes from an AlN target have been studied in real time by spatially and temporally resolved optical spectroscopy. The mean front velocity has been measured and appears to be slightly slower in the presence of added gas than in vacuum. In the initial stage of expansion, this velocity is almost the same for all neutral particles in the plume in the initial stage of expansion. Velocities of neutral and ionic species have been measured by their time of arrival from the target to a quadrupole mass spectrometer and their expansion beam Maxwell-Boltzmann (MB) temperature determined. The plume electronic temperature has been determined by assuming a local thermodynamic equilibrium of the emitting species.

Ablation of transition metal oxides by different laser pulse duration and thin films deposition

Thin films of transition metal oxides are of interest in many applications such as anticorrosion coatings and optical and electrochromic devices. In this work, the effect of different wavelength and pulse duration on ablation of oxides target has been investigated. The plume has been characterized by mass spectrometry and optical spectroscopy. Ablation thresholds have been measured by detecting ion emission from the target and from the onset of the plume luminescence. Morphology and optical properties of thin films deposited in different conditions are presented.

Anticorrosion titanium oxide coatings deposited by pulsed laser ablation

Abstract Titanium oxide coatings have been deposited on to iron and steel substrates, by pulsed laser ablation, to prevent corrosion from foods and corrosive agents. The films, deposited from laser ablation of a titanium target in a vacuum chamber containing oxygen, have been characterised by X-ray photoelectron spectroscopy to analyse their composition, and by electrochemical tests to study the homogeneity of the coating and its resistance to corrosion. X-ray diffraction analysis has been also used to study film structure. Laser fluence, substrate temperature and oxygen pressure have been optimised to improve the technological characteristics of the deposits.

STUDIES ON NITRIDATION OF LASER EVAPORATED III-IV GROUP ELEMENTS WITH GASEOUS AMMONIA AND THIN FILM DEPOSITION

Abstract Groups III and IV nitrides have been viewed as promising materials in many technological applications, mostly in electronic devices and in ceramic materials. Many techniques such as CVD and MBE have been used to grow nitride thin films. A method to prepare nitrides by adding gaseous ammonia to laser evaporated elements has been developed in our laboratory. B, In, Si and Ge nitrides have been prepared by this method. The intermediate steps in nitride production have been examined by optical emission measurements and by mass spectrometry of the gas phase. The final products of the reaction have been characterized on various substrate surfaces by conventional techniques such as SEM, XRD and IR.

Laser excited charge transfer processes in oxygen organic molecules mixtures : O(3Pj) formation

Abstract Laser induced charge transfer (CT) processes have attracted attention for many years. These reactions play an important role in chemistry as well as biophysics and biology. When the reaction is induced by laser on a complex formed in a supersonic beam, the impact geometry is well defined and reaction details are more evident. This paper deals with features relevant to O 2 photodissociation induced in clusters of oxygen molecules and rare gases, water or organic molecules. Our studies, performed in a supersonic beam by using lasers of different wavelength to induce the reaction and to detect the reaction products by multiphoton ionization, show that production of atomic oxygen is strongly dependent on the ionization potential of the electron donor.

Reaction of Al with ammonia by pulsed laser ablation: Optical analysis and mass spectrometry

Abstract In situ techniques have been employed to characterize laser plasma (plume) formation and reactions in the gas cloud formed from Al and NH 3 . Optical emission imaging and spectroscopy, and time of flight mass spectrometry have been used to monitor ablation plume components. AlN films have been synthesized by reaction of laser evaporated Al in a NH 3 atmosphere. Optical multichannel emission spectroscopy (OMA) and intensified charge coupled device (ICCD) imaging have been applied to identification of the deposition precursors occurring in the plasma.

Pulsed laser ablation: reactivity of photoablated neutral particles from FeCr alloy

Abstract In this paper experimental measurements taken in our laboratory on pulsed laser ablation of a FeCr alloy by Nd:YAG and KrF lasers are reported. REMPI ionization of the neutral Fe and Cr atoms formed indicates that the atoms in the excited states are not completely quenched when they are carried by the supersonic jet. The formation and stability of clusters of photoablated mono and diatomic metals with NH 3 molecules has also been investigated and the results show that they can generate electrostatic bonded clusters.